Why is my 6 month old waking up so much now?

He may be teething my son kind of went through the same thing. He was a great sleeper and around 6 months he started waking up again about 1-2 times a night. I figured out he was hungry. I didn't strt feeding him baby food until around the same age so I started adding baby food to his bedtime routine and it worked like a charm. the milk just wasn't keeping him full thru the night anymore. Teething is also a big factor. Maybe try some oragel right before you put him down. As for the sleeping on the tummy thing, my son started doing that too and there is no way I can keep him on his back anymore. I'm pretty sure the sids thing is on the downhill after 6 months and keeping a fan running in his room will decrease the chance for sids by 70%. And if you are really worried just take the bumpers off of his crib. These things should help you sleep more soundly. Good Luck.