Chiropractor could work wonders
I could never swaddle my baby boy either and I started using a sack at 2 months old and letting him sleep on his belly. He's very strong to lift his head up so don't do this without supervision if he doesn't lift head really good yet. I have a little crib next to me so i can watch him at all times. But overall he never sleeps flat on his back either
My son did this and I figured out it was congestion, he was born in spring so allergies were bad. I had to do sinus rinses a couple times a night to give him relief