Has anyone had a new born that’s been pushing themselves over since birth?

My sons 3.5 weeks old and he’s been pushing himself up and over to his back since birth. He doesn’t sleep on his back he has to be on his side or falling asleep on one of us on his tummy even then when we put him in the bassinet he rolls to his side. Makes me super nervous. Anyway, my whole question is, when should we expect him to start crawling? Will he be ahead of the average kid? I should mention he can’t roll back to his stomach and when we do tummy time he’s scouting forward but hasn’t figured out the arm leg coordination yet.