My back gets sore too.. If I were you I would start making a habit of going to the chiropractor, it is the only thing that gives me relief. Also getting registered massages is super nice too. I used to always sleep on my back and I have really struggled with sleeping on my side and find I have more back pain now than when I did sleep on my back. I got a body pillow it helps a lot, and might help you with getting some support on your hips, and you can even put it under your belly too. I would also keep warm but don't get too hot either.
Definately go to the chiropractor though, I go usually a couple times a month now and a massage once a month and it helps so much. :)