Why do I start my period early even though I'm on birth control?

Need to find out. I suspect you have an endometrial polyp, but this needs to be checked by your gynecologist. Good luck.
Bleeing on Pills. Some pills just do this and I don't know why this happens. I usually get an ultrasound to make sure there are no fibroids or polyps and then change them to a different pill with a higher estrogen for a couple of months then bring them back to a lower dose and this seems to work.