I had this the last 10 weeks too.
Your pubis is in fact two bones conected in the middle. Your joints soften and seperate a little to allow LO to pass through. Sometimes these two bones seperate too far.
It can be extremely painful. Try to take things easy, walking too much agravates it. When the pain is really bad, so bad you can barley walk try walking backwards. You could ask to see a physio about it but by the time you get a referal through you may be due. It maight be worth a try though, there is a belt you can wear to help.
Good luck.