L.L.
I gave up getting my youngest to sleep on her back a few weeks after she was born, because she just wouldn't.
I know they tell you not to let them sleep on their tummies, but mothers did if for probably a few thousand years before they came up with SIDS. And if you want reassurance, look at the actual statistics...used to be 2 out of 100 babies died of SIDS on their tummies, while now only 1 out of 100 babies die of SIDS on their tummies. Only what they tell you is "twice as many die" and they don't tell you about the babies who ALSO sleep on their back and die of SIDS, or that there are usually other factors involved (smoke exposure, illness, low birthweight, blankets in crib, etc.)
So, I put baby to sleep on her tummy and she slept better IMMEDIATELY. She was startling herself awake every 10-15 minutes on her back, and you couldn't swaddle her because she was too strong and active. She could hold her head up from birth, so I just figured, hey, I'm going to try this. It worked.
She's ten months old now and still HATES laying on her back, even for a diaper change. She does have silent reflux (reflux with no spit up) and that may contribute to the why, but anyhow.
Hope this helps...and I hope no one gets mad because I suggested letting him sleep on his tummy. I really think sometimes it's best.