So what was it then?

I had sex during my fertile window, i had dark brown spotting and mucus that I thought was period but it happened on CD 22-23 (7-8DPO) and stopped. I tested Negative at 9DPO AND Negative at 13DPO But since it was evening, and I tested with Walmart cheapies, and it was possibly diluted. I waited til this morning to use first morning urine at 14DPO my expected period day and a clear blue digital and still tested negative.

I’m ok with it being negative I just wanna be 100% sure. And understand if it wasnt implantation bleeding then what the heck was it?