Just wanted to say.. it can definitely happen before you even get a period!!
I have been off the pill since end of August, and have had no period, at all. I actually went to the doctor as I was starting to get concerned, I assumed no period meant no ovulation, which means no getting pregnant.
She said it can take months and up to a year to get a normal cycle back to not worry, but that I could get pregnant when I ovulate for the first time before a period even happens... .and I did!
So keep doing those ovulation strips, and keep aware of your body.. I just got my BFP last week and I did not get one period since coming off the pill in August :)