I have been on both before. Shouldn't be a problem. The Provera should help you shed the old lining you have, and hopefully the metformin will get you having cycles on your own. Good luck!
I checked the interaction and the only one between the two is that Provera may make the metformin less effective at controlling blood sugars, so diabetics should use caution. Lots of meds interact with metformin like that, but since you are using it for PCOS you don't need to worry. In the future, you can check out interactions
here