If the pain is really bad your hip could be out of place, you can try massaging it back yourself or go to a chirpractor. I get this every now and then, i just massage it every day until it goes away. To keep it from happening again try sleeping supported with pillows and with a pillow between your knees.
On top of that mine Pop every time I walk :-/ blah lol
Ok yes I have had terrible pelvic pain since 16 weeks the wonders of pregnancy!!