Hi.. Thanks for the query.. .. As per your complain for weight gain you will have to maintain proper nutritional supplementation to body through diet and also start doing muscle or weight training to gain muscle mass.. Also you should consult an Endocrinologist and get a hormonal profile, especially thyroid levels done.. You should eat a blend of carbohydrates, proteins and fats.. Add whole grains, rice, potatoes, sweet potatoes, ghee [in limits] and also paneer, tofu, eggs [if non vegetarian] and nuts in diet... Take proper sleep and drink plenty of water.. You can also be advised protein supplements but take only under supervision of a dietician and in calculated doses... Weight training sessions under a certified physician trainer can help in gaining muscle mass that will give you a bulkier look.. Hope this helps. Regards.