I have been on birth control for over a year. i started to bleed a week before i start the inactive pills i always use condoms. what can cause this?

Breakthru bleeding: Today's oral contraceptives are very low in hormones. They require a very punctual schedule to maintain the level of hormone needed to prevent "breakthrough bleeding" , so failure to take an active pill within an hour or two of the previous day can result in bleeding. Obtain a serum HCG pregnancy test . Taking the active pill more than seven days after the last does not prevent ovulation.