My Son Is Almost 4 Months Old. He's Starting To

My son is almost 4 months old. He's starting to roll over. Now when he's sleeping he rolls over to his side, and sometimes his stomach. I'm worried that since he's not really good at rolling back to his back that SIDS is in factor. Every time I put him back on his back he rolls back to his side. I can't sleep I'm so worried about him.