Implantation bleeding?

So I just joined a couple weeks ago. And searched all over Google but wanted to get you ladies opinion. I had sex with my soon to be husband on Saturday which was, according to my calendar, my peak fertility day. On Monday I saw a pinkish color when wiping and today it was a little darker. But didn't see anything on Tuesday. I've read implantation bleeding usually starts 6 days after implantation which it has not been that long. What do you ladies think? How soon can a pregnancy test show I'm pregnant?