I NEED HELP. PLEASE.

I had sex the day after my period ended and I took plan b the morning after. I haven’t had my period yet and I am 12 days late. I did have some brown slime type of substance come out. (The same consistency as when you have those “chucks” on your period, but brown. Not sure is that is normal but it went on for about 3 days) I took two pregnancy tests and they came out negative. I am assuming that I’m late because of the pill messing with my cycle. I just want to know if this has happened to anyone else and what the outcome was...thank you so much!