A sore pelvis is normal at the stage, everything is shifting around getting ready for the big day. If you still have these cramps though you should go get checked out. Like vins_girl said it could be an uti. At least if you get checked out you can put your mind at ease.
I went in for menstrual like cramps and my doctor told me I was ok, but it can be a symptom for some pregnant women when they have a UTI so you may want to get checked out.
Oh my goodness! I'm glad somebody is feeling the same way as I do. I was just about to post a similar question and then I saw this post. I am 33 weeks and 4 days by the way. I hope somebody can shed some light to this matter.