HELP!! Baby rolling while asleep!

I’ll preface by saying I know if baby can roll fine, if she rolls in her sleep you’re supposed to be able to leave them safely.. the only issue is she has stopped rolling from belly to back for some reason. She rolls on to her belly then cries when she’s had enough tummy time, she won’t roll back over to her back. Tonight while asleep she rolled on to belly so I went to check on her and her face was at an angle that was pointed towards mattress but I could hear her breathing fine. I flipped her anyway just to be safe. Not ten minutes later she’s rolled again! What do I do? I’m terrified!! (Baby is 4.5 months)