I definatly can relate. I'm 17 also, normal weight and 5'5. However my stomach is huge and it always has been. I remember the first day of ballet when I was little seeing everyone and wondering why the heck my stomach was so much bigger than everyone elses.
I've found dieting had given me more shape. I don't have a flat stomach but it definatly is improving. With the right cut and right fabric, you probably know you can hide your tummy very well. However that creates an annoying problem. When people ask why I eat cerial (healthy, low calories and fat) at lunch I say it's a diet. Now I've got people running around trying to help me with my "annorexic problem".
Anyway, I definatly store all my fat in my stomach, luckily though when I loose weight (I've lost about 10 lbs) I loose it from my tummy. I don't think having a not-so-flat tummy is the reason why you are having stomach pains, go see a GI because it may be totaly unrelated.
"Careful the things you say, children will listen.
Careful the things you do, children will see.
~Into the Woods