I have an Audi A6 Quattro (2006) S-Line

I was driving around the the centre backlight turns off and the service light for the "centre back light" turned on. If my car stands long enough, the light will turn on for at least 2 minutes when pressing my breaks, but then once again the brake light just turns off ,and will not come back on. WHAT DO I DO?! please help me i have been researching for hours and cant find a solution.