Hello how are you?
What is your height? The ideal weight of any person can be determined only after knowing his/her height. For weight gain and weight loss diet and exercise play an integral role. For gaining weight you should start eating the right type of food. Eat food rich in minerals, vitamins and all other essential nutrients. Stay away from fattening junk food. Try gaining weight in a healthy way. Exercise daily. Consult a nutritionist and get your diet chart made. If you still find it difficult to gain weight rule out worm infestation, diabetes mellitus and thyrotoxicosis. Do keep us posted.
Best of luck!