early period from plan b?

how early is your period supposed to start when you take plan b? i think i just started mine and it's two weeks earlier than it was supposed to start. i took the pill a week ago.

it feels like a little too much to be just spotting and at first it was mostly just brown colored discharge and now it feels like i'm on my period but idk.

this was my first time taking plan b so i just am not sure what is normal