Faint positive HPT, then negative HPT?

Ok, so I took an HPT yesterday afternoon and got a very faint positive. Then I took another one this morning with FMU and got a negative. The positive was an Answer (early detection) and today's was FRER. I'm confused! I'm expecting AF by tomorrow and not sure when I ovulated (I don't track it). I think I'm just going to wait and see if AF shows up by this weekend. I have never been late. I always have 28 day cycles. I have been having brown spotting off and on since Tuesday. Implantation bleeding? I have been experiencing every pg symptom for the past week and I don't feel like AF is coming. Anyone been pregnant with a faint positive, then negative?