pre-pregnancy my periods were always 30 days. Now they're 27, 28, 29- variable. My doc tells me that pregnancy can change your periods, but even the shorter cycle you described is still in normal limits. I think that anonvulatory cycles tend to be longer than normal, but that they can be the same cycle length or even shorter. I don't chart my bbt, but I've heard that can help you know when you have an anovulatory cycle bc of lack of thermal shifts (or something! maybe one of the charting gals can help with that). Also, maybe you just had a "chemical pregnancy" or very early miscarriage. I've heard those can be confused with a normal period.
Mama to Millie
born June 2010 @ 24 wks. gestation due to my severe PE and CHF
lived 25 days, loved and missed