I have lost a lot of weight since i was 17 ( when i took 4 courses of antibiotics) and till now i can't gaon any weight my body is not absorbing fats ?

Doctor can evaluate: If one is truly underweight (based on height, family background, and body type), a Dr. can evaluate for a hormonal, digestive, or other disorder. If no medical cause is found, then one can add weight by eating more calories of nutritious foods, while also doing weight-training to increase muscle. Proteins: egg white, chicken breast, salmon, ... Better fats: olive oil, peanuts, almonds, tofu, ....