I slept with my belt on, that helped a lot! I found sleeping with a pillow between my legs made me feel more uncomfortable. It was better for me to sleep the way I like, on the side of the stomach with the top knee in front of my stomach to support the weight (any side works for me). But when I was in a lot of pain I just laid flat on my back with the belt on.
When my back hurts I lay on the floor on my back with my knees to my chest and relax for a while. Just make sure someone is around to help you get back up just in case you get stuck like a turtle. And massages are always nice.
Stand on all 4 and have someone apply equal pressure on the lower back...hands on each side, or will relief pressure from the baby