It could be Symphysis Pubis Dysfunction, which google it and see if the symptons fit.

My sister had it during her last pregnancy and described it the same way as you, there is not much they can do to get rid of it because it is your hormones relaxing the ligaments that hold the pelvic joints.

Ask about it at your next appt, they can offer you physio exercises to do to strengthen the muscles, a belt to wear and hyrdrotherapy to help relieve the pain.

If can get worse with each pregnancy which is why the strengthing exercises are so important.