I had hip pain during and after my pregnancy. Particular if I slept on my side. During pregnancy your body releases the hormone relaxin that causes your joints and ligaments to loosen (particularly the hips) in preparation for childbirth, that combined with the pressure from the baby is what causes the problem. I try to sleep with a pillow wedged behind me to lean on to take the pressure off my hips. If I slept directly on my side I would wake up in the middle of the night in awful pain.
I also have hip pain but I'm not nearly as far along as you. Curious to see how to relieve it. It's in both of my hips and I haven't been laying on them.