You shouldn't get your period early on the pill if you've taken them correctly. Talk to the doctor that gave you the pills. You may need to be on a different kind of pill.
This has happened to me for two months already and doctor says it's okay. She did suggest that if it continues after three cycles that a change in pill might be necessary but I wouldn't try to change them before as your system could just be getting used to the pill and changing it might start things all over again. In a nutshell, if it's not too bothersome, give it three cycles if you can.
I'm on my fourth brand of pill now because of this problem. I take my pills every day, never missing by more than an hour or so (which only happens about once a month). It's usually just a matter of finding the right combination of hormones. My gynecologist also sugessted that if the new sample and prescription she gave me don't work, I should have my thyroid levels tested, and also suggested that I may have uterine polyps, which can cause something similar to break through bleeding. Also, if you're having this problem with a triphasic pill, you should try switching to a monophasic pill. It's one of the most frustrating things I've gone through since I've been on some type of pill for over a year with no luck with my bleeding, but I'm determined to stick with it.