How can I gain weight without it all going to my stomach?

I've always had a really fast metabolism and have been slightly underweight all my life. About a year ago I started eating a lot more (almost full meals every three hours). Because of this, I gained about 15 pounds, which I'm really happy about, but it's mostly going to my stomach. So now I'm still slim but with a small belly. I work out daily (15 minutes of weight training + 15 minutes of cardio). I do eat a lot of carbs, but I'm a picky eater and don't eat a lot of meat. Any suggestions? How can I continue to gain weight without it all going straight to my stomach?