Is Pregnancy Possible

The end of last month, my SO and I had sex for the first time. I'm not gonna lie, it started off unprotected (we got tested together beforehand) and towards the middle we switched to a condom because he didn't trust himself to pull out. About five days later my period started (two days late) and was lighter and shorter than normal. None of that really concerned me, I chalked it up to a new partner/New stress. However, for two days last week I had a light pink discharge that was only noticeable when I wiped. What are the chances of that being implantation bleeding?