Why Im I skinny? Please read if your bored!!?

Im 14 and I kind of look like a skinny african with a big belly. My family members are not skinny at all, Im the only one. I eat as much as them and lately I've been try to eat more then them but only my belly grows and my chest is flat. Im a guy and that isn't attractive to girls. I also have this pain that is between my chest (It only hurts if you push slightly) and abdomen and I still haven't told the doctor bout it. But ye, could I have some kind of bacteria or disease? Im always farting too! That sucks!!!! I HATE BEING SKINNY