Took plan b while on birth control, normal period a day after it was expected, 11 days later i had thick brown discharge at night now pink, worried?

I'm confused: Perhaps you are too. Why would you need plan B while on birth control? Also, having a normal period only a day late is not reason for concern. The discharge is approximately at the time you'd ovulate and brown is common at your most fertile time - so is pink spotting. What are you worried about? See your provider, have an exam and ask for lots of info. Learn as much as you can about reproduction