Is this implantation bleeding?

So a day or two after having sex with my partner (it was unprotected)

I started feeling like I have having bad peroid craps but I had just gotton off of my period the week before.

This amount of blood was in my underwear after the day of feeling like I was on my peroid but no more strong pains and no more bleeding since then...is this implantation bleeding? I'm not sure how long after sex that would occur or what this could be?