Sex brings on period

[themindbogglesallthetime]

I have pcos so have fairly irregular periods, back in July until the beginning of this month my periods started to come every 2-3 weeks, I was referred for a scan which I've had today, it came back ok (apart from a cyst on the right side of my ovaries and have to go back in 3 months). I now feel like my period is going to start, which is exactly how I feel after sex and sure enough the next day it starts. When I mentioned this to my gp she said she wasn't sure and just refereed me for my scan. (I haven't had sex for nearly 2 months and haven't bled at all) I'm on anti depressants and don't feel like it) not every time in the months from July until the beginning of this month it happened (we don't have sex that often) but it seems the majority of the time! Just looking to see if anyone else has experience of this or if it's just me?!
Also hope it makes sense and doesn't sound to rambled!