4 days late, still bfn I'm usually regular, periods only last 4 days. I have no sign of a period…

4 days late, still bfn

I'm usually regular, periods only last 4 days. I have no sign of a period starting. I've been having bad headaches (usually never do) all week and been constipated. Also, I can smell everything, have had some nausea and cramping at estimated 9 dpo that only lasted that day. Nipples sensitive on/off. Hubby and I bd almost everyday during my fertile window. I don't understand what's going on. Has anyone had this happen and got a bfp? I'm starting to think I'm not pregnant.