This will sound strange but give it a try. Sleep on your side with a pillow between your legs, and place another pillow at your feet for the bottom leg to be placed on. By doing this, you are 'neutralizing' the position your hips are in (pillow between legs) which also helps with the alignment of the musculature near your vaginal area (pelvic floor muscles). The pillow for your feet raises your leg slightly, shortening the pelvic floor muscles so they're not 'stretching' and get a break when you are sleeping.
I've had butt pain (piriformus muscle) and pelvic floor pain, and as soon as I started using pillows in this manner the pain has been greatly reduced. Basically you want to try to get the body parts either neutral or the muscles shortened, because usually if you're throwing one muscle off down there, other muscles are thrown out of whack too!
If you don't want a fortress of pillows taking over your bed, you can buy a body pillow or curved pillow. It may take a few nights of restless sleep to get adjusted to this but it WILL help.