This is my second pregnancy and I have been feeling pressure since week 20. It's really bad if I am moving around alot. I spoke with my doc about it at week 24 and he said the pressure is normal as the pelvic bone is slowly separating. He told me that as long as I am not having contractions (BH or other) or my water doesn't break then all is okay. He stated that for some women, the pressure is so intense it pretty much immobilizes them. .
I think it's pretty common. With my son I started feeling pressure at 29 weeks. Almost like he was going to fall out or something, but it has to do with the position of the baby. Things will be getting ready for delivery soon so new aches and pains are normal. If you are having BH in a pattern or spotting of any kind, then call your doc. I am only 20 weeks and the pressure and pain in my pelvis is unbearable at times.