Spotting a week after period + unprotected sex

I had my period last week which ended on Monday and had unprotected sex the same day where he pulled out.

just to be sure I took Plan B the next day. It is now 7 days later and I’ve been spotting since last night. Its a similar colour to my period, and I’m just feeling tired and experiencing light cramps.

Is this implantation bleeding?? or side effects of Plan B?? Im so scared!!!