I'm not a doctor, but think of it this way: if you hadn't been blessed with this glorious syndrome of PCOS, and if you were the most fertile lady in the universe, your birth control (and condoms, to boot) would still 99% effective or whatever their stats are. Metformin is not going to make you ridiculously fertile to the point that your ovaries are too strong for the BC pill to handle, especially with PCOS. I really wouldn't worry about it, but if you want some confirmation, talk to your doctor.
I've been sexually active the whole time I've been on Met & BC pills, don't use condoms (same boyfriend) and it's never been an issue. But everyone is different.
I also like that you used the word "hyperfertility" because I've never heard that used with Metformin, but gosh I wish it were true, cuz someday I'd like to get pregnant.
Good luck!