How to sleep without pain or cramp?

I'm almost 28 weeks and I'm trying to sleep on the side as much as possible. But after sometime sleeping the center top of my tummy feel cramp and pain which doesn't allow me to get back straight. It also feel like a burning sensation accompanied by the cramp. The only position im able to lie is on the back. But i know i can't sleep like that for long. I tried placing pillow underneath and using a maternity pillow to hug but it is still painful. Anyone have the same experience before? How do i overcome this?