2 questions

I took plan b and I got my period within the 3 weeks. I got my period at the expected time. Does it mean it work? I’m still on my period.

As I was in bathroom changing my pad and wiping myself to clean, I saw a long blood string which I don’t know what to name it nor do I know what it is. Even before that I got a blood cot which I also think it was a miscarriage. Or are these things different from being a miscarriage? The only thing that came through my mind was a miscarriage. Do you think it was due to taking plan b?