Remember while you were on the pill, the hormones in the pills determined when you had your period, not your body. When you go off the pills, you will be irregular until your body re-learns how to regulate its own hormones.
Also, your period will go back to its pre-pill schedule meaning if you were irregular before going on the pill, you will be irregular when you go off the pill.View Thread
Recently, I was well over a week late for my period and I wasn't pregnant. I had never been that late before either.
It's also possible you didn't ovulate and no ovulation usually means no period. It's common and will happen to most women at least once during their reproductive years. No particular reason for it happening.View Thread