advice needed!!!

Sarina • Mommy to a baby boy named Easton wife to a handsome man named john.❤️
Ladies I have a question? I'm 23 days late and I've took 2 hpt tests around 6 days late but just got tested at the doctors a week ago and they said bfn
I have no signs of starting my period note that I'm also 6 months pp. my periods have been on track since I got my first period after my son was born. It just now started acting up what could be going on? I've been keeping frequent headaches but other then that I'm not having any other symptom. 
My husband and I use condoms! But went twice without one. 
We aren't trying but wouldn't care for another one. 
Could anyone tell me what's going on?