It could happen if it was too rough. I don't think it's related to PCOS. Also if your a "small" woman that could be part of it too. I have been with my husband for 7.5 years and if we go more that a few days between "encounters" I feel like i'm a virgin again (sorry tmi) and I bleed for a day or two also. you should definitely tell your doctor about it though, it can be a sign of endometriosis and yes you can have both. good luck hun hopefully it's just that your small.
I don't think it is related to PCOS. I have PCOS and never bleed after sex, and sometimes my boyfriend and I go a week without having it and still I don't bleed, just feels tighter. I agree with wanabb that if the sex is rough or if the guy is a bit larger then what your body can handle, then yes you can bleed. Bleeding after sex could me other things other then PCOS as wanabb said it could also be endo. Still, you need to check it out to make sure it's not something worse.
I agree with wanabb and msniki412 about it not being related to PCOS. Now I do have PCOS and I do bleed/spot sometimes during/after sex. Now it all depends when we have sex compared to my menstrual cycle, earlier in the game I'm clear but later in the game with deep penetration I spot a little (sorry if its tmi). Now I have no idea why. 10 years ago I was diagnosed with endometriosis but, now the OB says she only sees the PCOS. Good luck with getting results. Just make sure you tell your dr. everything that concerns you.