Plan b

I have un protected sex twice in the time span of two days but he never finished inside of me. I took the plan B minutes after the second time. I have so far had two periods/ I’ve been bleeding the lasting three days in the last three weeks with a week in between. Is that normal? Because I’ve heard that plan b just messes up your cycle over all. Or could it be implantation bleeding? It was heavy and seemed like a normal period