My daughter stared rolling at 2.5 months. I was very worried becasue of SIDS. My doctor said that if they roll on their own, than they can get out of a precarious position. Of course I checked on her a hundred times a night for the first month and no matter how many times I put her on her back, she rolled right back to her stomach! Eventually, I just stopped worrying. She is now 7 months and as healthy as can be! I did not use a sleep positioner, because it is my understanding that once they start rolling, they can roll with it, and get trapped. That really really worried me.
Since every baby is different, I would call the doctor. They usually have triage lines where a nurse well versed in these types of questions can give you an answer, especially since your baby has acid reflux.
Good luck!