yep it's normal I'm only 25.4 weeks with my twins and mine has been like that for a good month now.
Wow girl, I was just thinking about you the other day. Just wondering how this pregnancy was going for you. I can't believe you are already 31 weeks.
Anyway, your belly is going to be hard because the baby is getting so big. That is also why you are having trouble breathing. They baby is taking up so much room and is very close to the diaphram so that is making it harder to breath. When this would happen to me, I would just try to sit straight to where my chest was open (so to speak) and take deep breaths.
I know it can be miserable, but you are almost there!!!