what you should do to increase weight is not to go to pills or supplements. it should be the food stuff increased consumption. increase the quantity of food per meal and also increase the no of meals consumed per day. than see in days how you will increase the weight.
Try putting on muscle. Eat alot of protein and work out. you'll gain alot if you keep at it. (Dont get discouraged if you dont see results at first, it takes a coupe weeks for improvement)