My 4month old sleeps on his side on his own.help!

Hello moma, my son turned 4 months yesterday and since 1 week he has been rolling from back to tummy.he still does not know how to roll from his tummy to back.lately since 3-4 days i have noticed that soon after i put him to sleep on his back ,within minutes he starts sleeping on his side.it worrys me alot.help please