Answer (Mag. nutr. Ivana Šimić):

Body mass index or BMI is used as indicator of an individual's nutritional status. It represents the ratio of body mass in kilograms to a ratio of body height im meters. Your BMI is 18 which signifies that the body mass is too low and it seems the concern of your nearest and dearest was right. Malnutrition leads to organism exhaustion and fall a lowering of immunity defence and it's recommended advisable to gain a few kilograms (at least 2 kg),  so you'd be within the normal weight/nutritional status range (BMI 18.5 to 24.9). The most important thing is that you shouldn't lose more weight.
More important than BMI value is the percentage of the fat tissue in the organism. Long term maintenance of fat tissue under 12% carries/brings health problems (amenorrhea, decreased immunity, slower recovery, decreased bone density and similiar). Some women experience problems when they fall below 16%. I would recommend you body composition checkup/test, concerning fat tissue percentage. You can test it in almost all fitness centres or the nutritional centre 'Adhara'. If you want your diet plan made, you can also contact the centre. You can find more information there.
It's important that you follow a healthy and balanced diet and harmonize energy intake with energy consumption. So no fast food, carbonized sodas, deserts and so on. Don't miss out meals and incorporate all food groups – cereals, legumes, seeds, nuts, fruit, vegetable and cold-pressed oils. A diverse diet ensures the required vitamins and minerals. Add healthy fats into your diet, eat fruit, dried fruit and nuts for snacks. An hour or two before training you should eat meals mostly made of complex carbohydrates (oat meal, brown rice, yam, quinoa, amaranth, whole wheat bread and so on), so you can provide your muscles with a continuous energy supply, and after the training it should be a combination of proteins and carbohydrates such as salad made of grilled mushrooms, cooked brocolli and cauliflower or tortillas stuffed with vegetables and chickpeas or green smoothie with added hemp proteins.
In the vegan diet we get proteins from legumes, cereals, seeds and nuts. You should keep in mind that seeds and nuts are also fat sources, so you shouldn't overdo (it) with their consumption.
To keep your calorie intake and consumption under control, I recommend you register on https://cronometer.com – the program is free and you can easily monitor your energy intake and consumption. All it takes is to increase calorie intake by 500 kcal per day so you could gain 0.5 kg per week.

Answer (Mag. nutr. Ivana Šimić):

The purpose of anticandida diet plan is to disable the reproduction of fungi in the gastrointestinal tract and must be implemented for at least 3 months. In addition to preventing the propagation of Candida it is also necessary to cleanse the body of toxins and strengthen the immune system.

The diet must not contain:
- sugar and all kinds of foods that contain it, including honey, maltose, dextrose, fructose, and very sweet, dry and canned fruit
- mushrooms and all kinds of foods that contain fungi such as cheese brie or camamber, beer, wine
- all products that contain yeast - the bread, pizza, yeast dough
 

Substitute cow's milk with soy, rice or almond beverage.
Cereals - consist of starch which breaks down into simple sugars in the process of digestion and is often recommended to exclude them completely from your diet at least the first week or two.

Gluten intolerance is often associated with the excessive growth of candida. Since it is very important to introduce a sufficient amount of energy, dietary fibers, vitamins and minerals, the diet should include gluten-free whole grains and pseudo cereals listed lower in the list. It is important to restore the intestinal flora with the help of quality probiotic.

It is also important to monitor symptoms and exclude the foods that bother you or cause problems.

It is especially recommended to consume the following on a daily basis: turmeric, ginger, garlic, coriander, tahebo tea and omega 3 fatty acids (flax, linseed oil, green leafy vegetables, nuts, chia seeds, hemp, hemp oil, etc.).
Nutritional supplements: probiotics (Lactobacillus acidophilus and Bifidobacteria), such as for example the Acidosalus in soymilk, Neem powder, Citrofit.
 

Vegetables:

YES: cucumber, broccoli, cauliflower, kale, spinach, onion, garlic, cabbage, lettuce, tomatoes, Brussels sprouts, leeks, artichokes, asparagus, celery, egg plant, zucchini, and especially vegetables that are rich in chlorophyll, i.e., green leafy vegetables, including barley and wheat grass

NO: mushrooms, potatoes
Moderately: carrots, parsley root, sweetpotato, beets


Fruits:

YES: green apples, grapefruit, avocado, lemon, lime, strawberries, blueberries, blackberries

NO: sweet fruit (grapes, melons, apricots, dried fruits, canned fruits, fruit juices).
 

Nuts and seeds:
YES: almonds, hazelnuts, walnuts, flax, pumpkin seeds, sesame seeds, hemp, sunflower, pine nuts
NO: peanuts and pistachios and cashews.

Gluten-free cereals:
YES: amaranth, quinoa, buckwheat, millet, teff, oat bran, wild rice
NO: wheat, white flour and products of the pasta type, leafy dough
Moderately: brown rice, oats, rye.
 

Beverages:
coconut milk, rice, soy milk, almond milk, soy yogurt enriched with probiotic culture
Teas: Taheebo, mint, ginger, chamomile.

Legumes:
Chickpeas, adzuki beans, lentils, beans, tofu.

Spices:
coriander, basil, pepper, cinnamon, cloves, dill, garlic, ginger, oregano, pepper, rosemary, thyme, turmeric.
 

Oils:
virgin coconut oil, olive oil, sesame oil, linseed oil, hemp oil.

It is certainly necessary to throw out food that contains yeast: Baker's yeast, yeast supplements, bakery products with the addition of yeast. The only sweetener allowed is stevia.
 

Meals must be based on a permissible vegetables, cold pressed unrefined oils, legumes, seeds and nuts, and a moderate intake of gluten-free cereals and fruit permitted.

An example of green puree juice (choose one or a combination of the offered ingredients in an amount stated):
Base: beverage made from rice, soybean, coconut, almond or water (1 cup)
Green leafy vegetables: kale, spinach, chard, lettuce, dandelion or coriander leaf (2 cups)
Healthy fats: coconut oil, linseed oil, hemp oil, ½ avocado, flax seeds (ground), hemp seeds (1 tablespoon)
2-3 walnuts, hazelnuts or almonds
Fruits: green apple, lemon, lime or berries (¼ cup)
Additives for thickening and stimulating the digestion: chia seeds, psyllium (1 tablespoon)
Ginger, cinnamon, stevia (as per wish and taste)

Answer (Mag. nutr. Ivana Šimić):

We cannot have complete control over everything we eat. However, reducing the use of processed products and choosing whole foods from organic farming, if possible from trusted local producers, is the best combination.
The basis of our diet should be whole, unprocessed foods that preserve the natural wealth of nutrients. The healthiest foods are the everyday foods like fruits and vegetables, legumes, whole grains, nuts, seeds, cold pressed unrefined oils and various spices.

High productivity of modern culture depends on a number of chemicals and digesting them through the food is inevitable. Washing and peeling fruits and vegetables can remove most of the pesticides, but it often removes the important nutrients as well. This is why it's important to choose foods from organic farming, which, in addition to preserving health, also preserve our planet. Most conventional pesticides and industrial fertilizers are prohibited in organic production of food, just like GMO foods.

Always read the declaration on the product, a simple rule of thumb is that the more unknown ingredients there are, the further away this product is from its original form and it is designed so that the taste, smell and look is more attractive to the buyer and that it lasts longer on the shelf.

A spray for removing pesticides from the surface of fruits and vegetables is by no means a replacement for the ecologically-grown food, but can be useful if you are not sure of the origin of the product:
1 cup water
1 cup white vinegar
1 teaspoon of baking soda

Mix the components and pour them into a glass spray bottle. Sprinkle the food from all sides. Leave on for 5 to 10 minutes, and then wash it off with plenty of water. 
For larger amounts, pour the prepared liquid in a bowl and place the fruits and vegetables into it.

Answer (Mag. nutr. Ivana Šimić):

Concentration can be improved by consuming omega-3 fatty acids found in flax seeds and oil, olive oil and rapeseed oil.
Avocado is also good for concentration, as well as blueberries and whole grains.

Answer (Mag. nutr. Ivana Šimić):

If you have a regular intake of vitamin B12, there is no need to check the levels, but it is advisable to get a test once a year just to be safe. 
Studies show that the iron status of vegans is usually normal, and iron deficiency is less common than among the general population. If you still feel concerned about your iron levels, consult your doctor to get a check-up.
To ensure good health in general it is very important to eat grains, legumes, vegetables, mushrooms, fruit, nuts and seeds, avoid smoking, alcohol and refined foods such as sugar and white flour, and be physically active. We recommend reading more about plant-based foods here. 
In conclusion, you should consume whole and diverse plant foods and supplement with vitamin B12.