Implantation bleed?

Shea

my fertile window was July 11-16. I had unprotected sex july ninth. eight days after unprotected sex, July 17, I had one drop of brown blood. a single spot. hasn't happened since. I usually get spotting, or light flow, after ovulation but not obe single spot, so that's abnormal for me. I do not take oral contraceptives. at all. What what does this mean to y'all? Implantation or breakthrough? This isnt my normal ov spotting.