Hello, welcome to Healthcaremagic. You need to mention your height as well. For a person correct weight is identified by calculating BMI. It is weight in kg divided by square of height in meters. Normal range is 18 to 25. If your BMi is below this range you can consider gaining weight. To do that you must have well balanced diet rich in proteins
, minerals and vitamins
. Eat lot of fresh fruits and vegetables. Avoid fast and oily food. Eat small frequent meals. Exercise regularly as it improves appetite. Wish you good health.