Period or no period after plan B ? Help please! Xx

Hello everyone - I was wondering I could get some advice.

A week ago I had ‘sex’ with my partner. The reason why I put it like that is because it was literally under two minutes if that (I know that doesn’t mean anything) and neither of us were even close to finishing. Anyway - just to be on the safe side as there were no forms of contraception I got plan B.

My period was meant to start today but for the past 5 days I’ve experienced dark brown blood/discharge which has been all over the place. My tampons look like I’ve been having a period but whenever I wear a pad nothing happens. Today I’ve experienced a more thicker brown discharge or blood - I can’t really tell.

I was wondering if anyone had any thoughts - the doctor did say plan B could possibly mess my period around but I can’t tell if this even is a period.

Thank you everyone xx