Late AF

Samantha
Ok so my husband and I have been ttc and af was suppose to be here the 26th.   This is our second and with my first we weren't really trying to conceive but weren't stopping it.  By the time I realized I could be pregnant I was already a month late. This time I took a test the morning af was suppose to show and it was BFN.  I still haven't started and I'm on my forth day late.  I know I should retest but am waiting till Friday.  The other thing that makes this so confusing is when my son was 9 months I thought I was pregnant.  Two weeks late on af arrival but the test were negative.  Doc told me I prob just didn't make an egg.  Had a few months like that then everything went back to normal with monthly visits from af.  So I'm just wondering if anyone else has some insight or has dealt with this.  Thank you ladies.