If you had your period whilst still taking the hormones pills, and you didnt miss one or take it at a different time of day, then it is breakthrough bleeding and usually happens because the doseage isn't high enough - ie you are on 20ed, but may need to be on 30ed.
This happened to me, I ended up on 50ed Go to the doctor, they will most likely take you off them altogether, allow your cycle to regulate again, then start you on a stronger pill.

GL!