I'm not just trying to be nice, but 110 is a totally normal weight for 5'2, maybe even underweight for a guy. But maybe you just have a small frame? You're only 13 so it's completely normal, but if you really see it as a problem I suggest just getting more involved with sports. Join a team at school or invite some friends over for football, basketball, whatever you like. It's important to just be active and before you know it you'll lose the baby fat.