Period after stopping Birth Control

I've been on BC since the end of 2005, so close to 4 years now. The original reason I went on it was for extremely irregular periods (right before I started them, I hadn't had a period for 6 months). There are a few collective months during those years where I didn't start it on time, so I just didn't take it for that month, but I always had my period on time for that month, which always surprised me. This month, I was moving, traveling, starting a new job and school, and starting the pill slipped my mind again (oops >.<). I've been curious though, are these periods I have when I'm off the pill actually caused by ovulation, or is my body just doing what it's been told to do for 4 years by these little pills? I know for a large number of women, it can be up to a year after they stop taking hormonal BC before they have their period, so I would like to know why I, with my history of irregularity, remain regular when off BC. Maybe I would have to wait two months of the pill to really know for sure?