I was sitting up right in a chair and I tried to sit back when I got a cramp in my stomach and I feel my stomach a little bit hard when I'm standing up. I'm 15 weeks pregnant and I what to know if this is normal or should I be worried?

It is probably normal, You're going to feel a lot of things change. Chances are your uterus is starting to grow beyond your pelvis. It is all a part of the miracle.