I've been on birth control for 6 months. never missed a day. last two months my period has been irregular, comes and goes, and lasts more than a week.

Breakthrough bleed: Oral contraceptives are given on a monthly or an extended cycle. An extended cycle regimen reduces the number of episodes of withdrawal bleeding per year and can completely eliminate these episodes. The hormone-free interval may be 0, 2, 4, or 7 days. Shortening the hormone-free interval may reduce symptoms associated with hormone withdrawal.