I'm on my third kind of oral contraceptive now. The last one, orth-tricyclen lo, I stopped taking after about six months, because I experienced breakthrough bleeding during several consecutive cycles, even when I was good about taking it. I've been on Yaz for about a year, and I'm seeing breakthough bleeding again. This time, as opposed to typically seeing it BEFORE my period, I'm seeing it a few days after, as well. Right now, it's even kind of heavy, nearly black, and, um,...chunky. I admit that I am pretty unreliable with my pill, and have missed a few days this month. I know that missing days makes the pill less effective during that cycle, and I back up accordingly, but can it make the pill PERMANENTLY less effective, i.e. will missing a few this month lead to constant breakthough bleeding in the future? Is it possible to develop a kind of immunity to the pill, like bacteria does after an incomplete antibiotic run? I'm just worried that my body is going to stop responding to Yaz, as it seemed to do with ortho, and I'm going to run out of pill options.