The bleeding is most likely due to the fact that you missed 3 pills. This is a very common side effect when pills are missed.
If you had unprotected sex during the time you missed your pills or after this, however, you could be at risk for pregnancy. I would suggest using a back-up form of birth control or abstaining from sex for the rest of this pack and at least 7 days into the next. This is because your missed pills could cause you to ovulate later in the pack, esp during the placebo week. Once you have been on a new set of pills for 7 days, you will be fully protected again.