I think I had the same pain yall are talking about. It like started from the bottom of my belly and went up past my belly button in a straight line. I asked my doctor about it and he said that it was a muscle. Basically the baby stretches you out so much that simple activities like walking or doing house chores can strain some muscles and that it was totally normal. Still ask your doctor and show them where you're having pains and they should be able to tell you more. :)
I'm 36weeks and will be 37 on Sunday I get that pain to but I have no idea what the cause of it, sorry I can't help with the cause.