September was my first month off birth control.  I had my last period start on Aug 26th.  I assumed I have about a 28 day cycle because I've always been pretty regular but never tracked my period before now.  Assuming a 28 day cycle, I was supposed to start this past Wednesday, sept 23rd.  I took a test on the 23rd but it was clearly negative.  I still haven't started AF.  I ddon't think I'm pregnant but how am I supposed to know when I ovulate or when I'm fertile if my period isn't starting?  Advice please.  Thanks!