D.B.
I don't think that's surprising at all. Your natural cycles are trying to regulate themselves and there's no reason to think that you would remain on a 28-day cycle indefinitely after discontinuing the pill. Your ovaries are learning how to ovulate after 7 months of being shut down, and every woman's body will work on its own schedule in this regard.
What you do have to be more vigilant about, however, is recognizing that you have no idea when you are going to ovulate. That means you need to be extremely careful about using very reliable birth control unless you are trying to get pregnant. Your cycles are irregular at the present - not that timing and "rhythm" are good methods anyway, but they're even more iffy in your situation. So assume that you are fertile every single day. That's advice we always gave our patients when I was a birth control counselor, and it's good advice to remember.