I have been on everything from OrthoCyclen to YAZ and this extra ...

I have been on everything from OrthoCyclen to YAZ and this extra low-dose pill has been the only thing that I can remotely tolerate. I am, however, having some trouble with my cycle. It seems as though every other month, I start this really light period ONE WEEK early. I'm only coming up on my 4th pack, but I can't figure out why it's doing this. This is the only pill I've ever had this happen with. I'd much rather have some light spotting for 2 weeks than to be crazy and psychotic! If anyone else has experienced this, please reply. Was there a pattern????