Sleeping through the night?

My 7 month old son sleeps on his stomach, it doesn't matter if I lay him on his back, he just rolls over and sleeps on his tummy. The problem is that he wakes up every morning around 4-5am and needs his diaper changed because his clothes are all wet because he peed through his diaper. I change his diaper right before I put him to bed too, just wondering if there is anything I can do. If his clothes were not wet, I really don't think he would wake up until 7-8....