There are special "pillows" that are supposed prevent children from rolling over at night. I bought one from Target for my son when he was just a baby. It kept him on his back, even when he was able to roll over, and he was a "swaddle me" baby as well.
I'm not sure what you are swaddling your son in, but have you tried the Halo swaddling/sleep sacks? The swaddling feature is removable, but there is enough space for his legs to move around so it lessens his chance of possible kicking out and causing him to roll over.
I'm just throwing out some suggestions.
You could also call your pediatrician for any suggestions.
I hope you find your answer soon!
P.
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