While pregnancy is one possibility, there are a few other conditions which could cause this as well.
Ovarian cysts can block the normal production of hormones and could cause the body to stop menstruating or shedding in the case of being on the pill. The bcp you're taking may be too strong for you (your body changes as you get older and normal hormonal variations may have caused your period to stop).
Fibroid tumors (benign growths in the uterine wall) can also cause a disruption of the normal monthly bleeding.
Finally, some other diseases like thyroid conditions or ovarian cancer can cause disruptions in a cycle, even one regulated by the pill.
Please see your doctor to rule out one of these more serious conditions.