I know babies are supposed to sleep on their backs, but mine keeps turning over on his tummy. What should I do?

How old is your baby? If she can roll back herself from tummy to back already then you no need to worry about. If baby is younger, try to adjust her sleeping by placing her on her back instead of tummy to reduce SIDS risk. Your baby should sleep on a firm surface that’s covered by a tight-fitting sheet. There should be no loose bedding, soft pillows, or stuffed toys in your baby’s sleeping area. http://www.babysleepsite.com/tag/baby-sleeping-on-stomach/