Weird discharge or period?

Okay so I recently took plan b and I was feeling normal just more tired than usual. Today I went to the restroom thinking I needed to use it but then I saw this very dark discharge. I honestly thought I shit myself but I checked and didn't. But then when I wiped ya know it was pink? I'm hella confused if it's just weird discharge or my period. Does anyone know if the plan b is working or not? And should I be worried?