catherine, I too had this problem, and like lorasha, I had to do the 12-point turn every couple of hours!! The only thing that worked for me was to sleep in the spare bed, which has a really soft mattress. I think it was a combination of being able to sleep by myself (instead of with DH) and sinking into the mattress that helped. I'm not sure if it was good for me to be sleeping on a soft mattress, but it worked.
Good luck, hope you find something that works.