(( VaginaPagina ))

I'd look at breakthrough bleeding -- it's perfectly normal for people to stack their pills (take more than one pack's worth of active pills without taking the placebos), and it's equally normal for a bit of breakthrough bleeding to happen now and then, even if you can usually stack without a problem. The extra stress of a yeast infection might've prompted it, or you might've been a little late with one pill, or the phase of the moon and the lottery numbers might've had mystical influence upon your uterus. (I.e., sometimes stuff just happens and Bodies Are Weird.)

I hope that the treatment worked, though!