It can take a while for your periods to really get back to normal, I think it took my friend about a year to fully be back to normal.

I recently was off BC for 3 months by accident (didn't order my refill in time...won't do that again!) but I was off of it for so long because I never got my period in those 3 months. Finally, I went to the doctor and she said as long as a pregnancy test came back negative, I could start back up immediately. So I have no idea how long it would have taken for me to finally get a period. FWIW, I went on BC at 19 and before that my periods were anywhere from every 30-60 days, so they've never been regular.