Should I be concerned/go see the doctor?

I track cm/log my cycles on a calendar. I typically have a 26-27 day cycle. With CM, everything was moving “as planned.” Period was due Saturday (9/14)— and I noticed just a brown discharge. I thought, “okay cool. Period is coming. It’s just a weird cycle.” ..... 5 days later, I still have that same spotting. It is Brown with zero red/pink. It is also not enough to even need a liner (though I have been wearing one for precautions).

I had unprotected sex; tested BFN this morning. I still get heavy nausea and am fatigued (running TERRIBLE times lol despite my experience/ am just SO exhausted when running).

Is this cause for concern? After 5 days, should I go see a doctor?