Hi hun,
We had this issue, around 4 months, and literally the only reason dd was waking was as you described, when she stirred she would sleepily roll onto belly, when there woke up, realised stuck & cried out as couldnt get back and would not settle on tummy.
I spent many nights going in several times and turning her back thinking she would cotton on & just stop rolling! But after about 2 weeks (and she still couldnt roll back) i ended up looking up something called safe-t-sleep, which is a strap which straps them in position (on back, or side) and they cant roll. Another bw reccomended.
I looked it up and bought a snoooze (i think its called) which is exact same thing as a safe-t-sleep. First night she went in it, she slept all night long & is 11 months now and is still in it. I plan to remove it when she can roll out of it due to her becoming stronger or when she can actually open it!