At night time, your buttock muscles are less active due to being in a resting position. And depending on how you sleep, your joints may be in a more vulnerable position. Try icing your joints and applying heat to your muscles before you sleep to reduce pain. (You can also take a warm bath, or use a heating pad for no more than 20 minutes). You can also try using a pregnancy pillow or regular pillow between your knees to reduce the pressure on your pelvic region.