Sounds like AF to me, but then it's strange it was early and was so light. I have never had implantation bleeding so can't give much advice but I didn't think it lasted that long, which is why I think unfortunately it sounds like AF.

If it was implantation bleeding and it started over 5 days ago then at a guess it would say it might be early enough to show on a HPT?

Strange things can happen in the world of TTC! Good Luck!!