Please advise; Weight gain

I currently have a bad problem. I am currently 15, 6'1 in height and I weigh only 150 pounds. Thats not healthy for me. I use creatine and it works with muscel, but the main thing I want is to have a wider stomach area. Its really embarrassing of how it is. Anyone got any help for me? I need a written out schedule or something for eating so that I know how much to eat.