13 DPO AF Late BFN

Hello! First time posting here. I'm 2 days late on my AF and thinking I'm about 12-13 DPO. I have been tempting and tracking. My period is super regular. I'm getting very light brown inconsistent spotting, only when wiping and not always there. Sore breasts, which I never have. Been testing but getting BFNs. What could this be? Anyone else experience this? Test positive after  13 DPO? Looking for similar experiences.