HI,
I have a 9 month old and have have three cycles since her birth. Before she was conceived I was set the clock by it 28 day cycle, since bleeding again they have been getting later and later each month, to the point where each month I am convinced(and a little freaked out) that I am UTD. Last cycle it was a week late. I am just going to be on mucous watch from now on as I think the day counting will be way out. If you can wait it out for a week and test again, if symptoms start then test again perhaps. Mystery cycles are so frustrating, my DH ignores (in a loving way!) me when I start the I think I am UTD talk! haha