Ok so, for weeks I know I've been getting some contractions, and I know I'm already at least 1-2cm dilated, but I have a question?

With labour contractions, where does the stomach go hard?? I have extra fat on me, which when I sit up, gets pushed down by gravity (ITMS?)
But when I get contractions ATM, (im sitting up), the top half of my stomach goes ROCK hard, and I get period pain lower (in the usual area) for about 15 seconds or so, which gets more and more intense, then tapers odd and goes away.

But the bottom of my stomach doesn't seem to get as hard? It does go hard, but not as hard, I know she's bum out (face to my spine) so could that have anything to do with it? (I.e. Shes somehow pushing herself out, despite not being able to feel it)

Just confused and being a first timer to this i don't want to get myself excited unnecessarily

Thanks ladies!