I can understand your concern.
You haven't mentioned your weight for us for reference. Even your height is required.
Inability to gain weight should be evaluated and all other causes like hormonal abnormalities should be ruled out.
Syrup. Aristozyme 15ml twice a day immediately after food and syrup. Apifeast 10ml thrice a day 15 mins before food you can take.
Have a high protein diet and have frequent meals.
Consult a general physician in person for further evaluation and management.
Dr. Anil kumar jain.