The two months that I was on BC (biphasic, 50-to-1 progest/estro ratio) I bled every other week. Doctor said this was normal until my body adjusted to it, and to "not worry" unless it was still abnormal after three months. I stopped taking as it was stalling me, made me feel terrible and from what I've read hormonals have some screwy long-term effects. YMMV.