Has this happened to anyone? Opinions?

Hi everyone! I know everyone is different and all that I can really do is wait it out but I’d love to hear some opinions on this.

So I have multiple apps to chart my cycle. They all say just about the same thing, that my fertile window was from the 8th-13th. I BD’d on the 11th and 12th. On the 18th I had light pink spotting mixed with CM accompanied by little dull cramps. I checked back about 15mins later and the pink had darkened a little and then I checked again about an hour later and it was just brown when I’d wiped. Nothing after that. Could this have been Implantation bleeding? AF isn’t due until the 27th.

I appreciate any responses, thanks in advance.