Hi, Cerazette is not the typical birth control medication in that many regimens of birth control are a combination of Progesterone and Estrogen, but with Cezazette only a progestin medication is given. This can cause a lot of unusual side effects if one or several doses are missed. Often times menstrual flow will occur and unusual times or symptoms similar to pregnancy will begin then end abruptly. Medically speaking it produces a condition called dysfunctional uterine bleeding and is due to an imbalance in the progesterone / estrogen levels. This is a normal occurrence when the Cerazette is stopped mid-cycle. Returning to the normal dosing will return you to a regular cycle, but it does take 1-3 months before the regularity returns. I do understand the worry here, but give it a little more time. It doesn t sound like you are pregnant at all not with 2 negative tests. To be sure repeat the test once more and if negative then resume your normal regimen. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. David Girardi, Internal Medicine Specialist