Implantation bleeding

When would implantation bleeding occur? I’m due to get my period in 3 days and I bled a little today but it was very light and the last times I had sex were Friday 8/2 and Wednesday 8/7 but he didn’t cum inside me either time so I’m probably just freaking myself out but I was curious if it could be implantation bleeding. When would implantation bleeding occur? Thank you(: