Hi Pankaj, welcome to HCM.
You have not mentioned about your hieght and weight. Do not go for anything which will have side effects. If you do not have any other allergies or medical conditions you can try changing your diet. Include a lot of carbohydrate
intake in the form of rice, idlis,dosa,corn
flakes with almonds etc. Also increase your portion size. Consume more of dairy products such as milk, ruch curd, ice creams, cheese, butter, ghee etc. Losing weight is tough but to increase weight is easy. Have at least 8 hours of sleep and a regular routine. Also, you can include more nuts and dry fruits between meals which will help in weight gain. Good luck to you !!!