Now the problem is that this joint, unlike all the other joints of the body, dose not have any cartilage to protect the bone surface. Therefore when this joint moves the two parts of the bone rub against each other causing pain.
Sorry to be picky, but this isn't quite true. Between the two parts of the pelvis that meet at the front there is a cartilage disc and it is the torsion of this disc and the ligaments of the pelvis that causes pain.

I second the suggestion of taking careful strides, getting in and out of car carefully etc. If the pain persists or gets worse I'd go and see an osteopath or physio who specialises in pregnancy care.

Good luck!