Plan B

So I took plan B like within a half an hour after unprotected sex.

Okay full background, I had my normal period, had sex the day after I got off of it. A week later, I get another period from plan B. So it clearly works, but it's the heaviest flow ever, sometimes it's all black on my tampon or even brown. It's gross. I don't really smell anything though. I need advise, or does anyone know when it will end lol