Sleeping on your back while pregnant???

Having a hard time sleeping on my side in my third trimester. I have a sprained rib and so it's super uncomfortable for me to sleep on my side. Lately I prop my pillows up so I am not flat out on my back. I heard your not suppose to sleep on your back at all and read your baby can be still born If you do. What are your thoughts? Anyone else have issues with sleeping on your side?