You may have not ovulated and usually no ovulation means no period. It's common and will happen to most women at least once during their reproductive lives. Just because it's never happened doesn't mean it can't/won't.
If you miss a second period and are still getting negative tests, see your doctor.View Thread
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