not feeling pregnant? is that common

I know it sounds dumb. Maybe I'm freaking out for nothing. I'm 15 weeks with my third pregnancy. I haven't started showing (I did with my 2nd) yet and I'm 125 pounds. So you think the only place it could go is out. I haven't heard a heartbeat yet (and that's because I haven't had a dr check it yet) I did have an ultrasound at 9 weeks and everything looked good. I realize a lot can happen from nine to fifteen weeks. Should I be concerned? I've had no bleeding and I just don't feel any type of pregnancy symptom at all.