Three weeks late, BFN, light spotting

Diana
I've been a little worried lately, we have stopped TTC the last couple of months. Now my period is 3 weeks late. I've taken 3 HPT, all BFN. I have no pregnancy symptoms either. My periods have been regular the past few months. I noticed some pink coloring when I wiped after sex, and it's slowly turning brownish/reddish, but not very much. My boobs usually get sensitive/sore before my period, but nothing this month. What could this be??? Anyone else have any similar situations? Help!