Bleeding after sex

So last night we had amazing sex and for over an hour and I didn't bleed and then today we have a quicky and I start bleeding. I have PCOS and I know I am ovulating. Is it because we had sex two days in a row. I know I didn't pop a cyst because I'm not in any sort of pain. And no I don't have any std's. I see my obgyn regularly and I'm clear, my fiancé also gets testing done at the VA so he's good too. I just don't understand why sometimes I bleed and other times I don't. Any wisdom?