Intermittent minor menstrual bleeding could mean that your pill isn't strong enough, or it could signal a pelvic infection, endometriosis, or ectopic pregnancy. Once your doctor has ruled out these more serious possibilities, he or she will either switch you to a different pill (probably one with a higher dose of progestin or one of the new progestin pills) or counsel you to try to tolerate the bleeding and spotting for a little while longer, especially if you just started on the Pill. Breakthrough bleeding and spotting diminish rapidly over the first four months of pill use.
Most physicians do not recommend stopping the Pill because of this side effect. If you have any doubts, however, call your doctor.
