My menstrual cycle normally lasts 3 days, i have been off birth control for awhile but recently got back on since becoming sexually active again my most recent menstrual cycle has been going for three weeks now with one or two day breaks between.what is

Irregular cycle: This could be caused by just about anything, but you need to see your doctor since the bleeding has persisted.

Beakthrough bleeding: If this is your first cycle back on the pill this is probably what we call "breakthrough bleeding" and will tend to improve and resolve with future cycles. In that case you need only to stick with your pill as directed.