My son won’t sleep!

My son has mastered rolling over onto his belly. Now when I put him down to go to sleep he instantly flips over onto his belly with his head up. No matter how tired he is once he is on his belly his head is up and he is alert and if his head is not up his face is buried and he looks like he can’t breathe. I can’t sleep because of this because I’m constantly watching and worried about him! What do I do at this point because he’s driving me bonkers. I just want him to sleep. I just want to rest.