Ladies I'm on birth control but I'm taking my last week of my pill and it's the brown pill of the…

Ladies I'm on birth control but I'm taking my last week of my pill and it's the brown pill of the birth control which is my period pill this week, I have 3 more days of the brown pill and I haven't started my period yet!! This has never happened and I've been on this for awhile now, what should I do??