Doctor Answers (5) on Getting weight
You did not mention your height, any family history of such a stature, check your hormone levels or any other ailments with physician.
Have calorie dense yet nutritious foods like wholesome cereals like atta, oats, Dalia, jowar, millets. Milk, dal, sprouts, if non veg then eggs n lean meat n fish. Banana milk shakes, smoothies, soyamilk. Dry fruits like dates. Have lots of fluids. Sleep well. Reduce stress. Exercise daily.