What Causes Vaginal Bleeding Post Unprotected Sex Despite Being On Birth Control Pills?

I have been on birth control for over a year, and had unprotected sex. This has never happened before but yesterday morning I woke up with browny coloured stains in my underwear and throughout the day I was getting terrible headaches and migranes (which I don't usually get) then during the evening when I went to the toilet I noticed a orangey colored discharge stain in my underwear but it didn't smell and my vagina has not been itchy. Is it blood?? Throughout the day today I have had normal coloured discharge but I've still been getting headaches and migranes (I don't know if they have anything to do with it though) but I went to the toilet a few hours a go and the orangey stain was back. What is going on? My period is due in a week but nothing like this has ever happened before