How Can I Gain Weight If I Have No Appetite And Is Nutrigain Powder Effective?

Question: Hi . I am 26 years old . My height is 165 cms and weight 53 kgs . I want gain weight . I look very weak and not like a 26 year old at all .I want to try rich foods but I don feel hungry most of the time . So i dont eat properly. I don have any other acute illness or disease. All my medical reports are good . What treatment is best . Nutrigain powder is effective ?