AF is 6 days late!

My husband and I are TTC! I finished my BC in December and had my regular cycle on 12/20. I used CB opk and when I had the solid smiley face, my husband and I BD'd for 2 days. I then had light pink and brown spotting (not enough to need a liner) 4 days before my cycle was due, which was 6-7dpo. I've never had spotting between cycles before. I had that light spotting off and on for 4-5 days. Now AF is late 6 days and I got a BFN on the last time I tested, which was Friday morning.  I'm going to retest tomorrow morning since I will be a week late. Has this happened to anyone? Was the light spotting that I had before my cycle really AF? My cycles have always been very predictable so maybe now that I'm not taking BC, I'm finding that they are irregular.