This cycle I had the exact same thing happen to me and I don't know why. I suffered a m/c in June and this was my first cycle since the m/c, so I don't know if that was the reason or if my hormones were acting up for another reason. I am not being monitored, so I don't know why and my acupuncturist wasn't sure either. Sorry this isn't very helpful, but know you are not alone.