Period is a week late, plus other drama.

So I had sex with this guy last Thursday unprotected, he didn't ejactuate inside me but just in case, I took a plan B pill Saturday. Anytime that I've taken the pill in the past, it was always the same day so that does make me feel a little nervous. On Sunday, I had sex with my, on again, off again BF. He knew about the situation and took it as his free oppurtunity to ejactuate inside me without me getting pregnant because I had took the plan B pill the day before and he assumed it would still work. A short while ago (it's Friday now, 5days later), I went to use the restroom and I noticed some spotting. Could this be implantation or is my period coming on?