what is going on with me?

I got a positive opk on 9/14. On 9/21 I had lower ab cramping that was very centered. 9/22 through today I have had on and off spotting, only noticeable when I wipe, and not every time I wipe. Today is cycle day 28, but Wednesday is 14 days after positive opk. I have an elevated temperature (99.1) which is super weird for me because my temp runs on the low side (97s). I took a pregnancy test but got a BFN. What is going on with me? Has anyone experienced anything like this?