TMI but I'm a desperate FTM!

I am 31 weeks 4 days. The baby is measuring 2 weeks ahead (I don't know if that matters, I just figured more information couldn't hurt). I'm 100% sure on when my period last was so I'm thinking the babe just had a growth spurt. Anyway, I've dealt with the normal constipation this whole time but this past like 4 or 5 days, I'm not necessarily constipated but all of the sudden I get insane rectal pressure and when I try to poop it kills. I'm sitting in the stall at my office trying and it hurts so bad. This can't be normal right? Any help is appreciated.