FTM Question.

Brittany
I am 35 weeks, it is uncomfortable to sit or lay on either side. My entire belly is really tight and if I get up quick then I get cramps like I would if I'm on my period and move to fast. If I happen to sit up I have to be leaning back in the car or chair I'm sitting in because I can feel the belly pressure all the way under my boobs and the only 100% way of being comfortable is being in a pool where I feel weightless but THEN once I get out of the pool my belly automatically pulls down and feels like my butt is about to fall to the ground. I have not experienced constipation during my pregnancy at all until this past week and I can sit on the toilet for 30-45 mins and not have a BM at all but still feel like I am about to poo my pants. Is this normal? Should I be concerned?