Confused. Opinions?

My husband and I are in our first month of TTC. AF was due Monday. I thought it was a good sign because I always have sore breasts the days leading up to it and I had no signs or symptoms. BFN Monday morning and then I had brown spotting later on that day. It turned into bright red in the evening and all day Tuesday. I assumed it was AF, as I also had very mild cramping. But it has not gotten any heavier and I haven’t needed to use a tampon- it’s just there when I wipe. Cramping also never got worse as usual and boobs never got sore. I just don’t understand why this is so out of the norm for me and what could have caused it to happen?