Hello, Thanks for choosing health care magic for posting your query. I have gone through your question in detail. Your weight and build depends a lot on your genetics. If your father and mother are thin built then it will be never possible to gain weight and build under normal conditions. Secondly ones build is also determined by your basal metabolic rate and if thats high, no matter what you eat, the body wont catch up. You should get a thyroid level investigated. many times hyperthyroidism is a reason for a low weight and if it is present it is correctable. Eat healthy food with lot of proteins like egg chicken etc. Do regular workouts. In some patients Syp Cyproheptadine has helped you could try it ones. Hope I am able to answer your concerns. If you have any further query, I would be glad to help you. In future if you wish to contact me directly, you can use the below mentioned link: bit.ly/dr-srikanth-reddy Wish you good health, Dr. Srikanth Reddy M.D.