Yes it is common for your pelvic and hip joints to loosen up in pregnancy getting ready for childbirth. The joints have to be able to "stretch" and it is very possible that you feel this. If this is uncomfortable you can try lying on your side with your legs crossed or with a pillow between your legs to relieve the pressure. Also you may be feeling your round ligaments stretching wich are between your pelvis and hips. Don't worry it is all normal. You are almost at full term so just try and hang in there!