Forget about the mass gainer and eat more, i know you try to eat as much as you can but try to eat more.. Heres the secret, try to get 5-6 meals a day with complex carbs and protein in every meal, For carbs eat oats, brown rice, whole wheat pasta, whole wheat bread, potatoes, for protein chicken breast, steak, tuna, eggs, turkey breast etc.. Try to get lots of carbs (the ones that i mentioned) and protein combine this with heavy weight in the gym and you'll see results very quickly, i tried this myself and it worked..