Hiya
I have PCOS too, I came off the pill (after 13yrs) and it took about 3mths for my period to return. I then had very irregular periods for 11mths when I fell pregnant. Unfortunately my son was stillborn at 24wks. However I fell pregnant 3mths later (without even TTC) with my daughter who was born this year.

Basically what I am trying to say is that it could take a long time but equally it could be very quick. You say you have on average 2 periods a year, it could be that you come off the pill and then immediately ovulate and fall pregnant!! I would personally come off the pill but use another form of contraception - especially until you have finished your exams. The last thing you will need is being pregnant during exam time - not just for the stress, but have you thought about morning sickness and insomnia!!!

Good luck with your decision.
Tess.