my hips hurt so bad!!

Tyler • Mommy of an angel baby👼🏼 baby number two is due March 8, 2017 so blessed and thankful! Thank you Jesus!
I'm 29-1 . And I normally sleep on my left side or right side , but lately I'll wake up in the middle of the night and my hips hurt so bad .. I have to lay on my back for awhile cause they hurt. Any idea why they do this?