Since i've been on birth control i've been having brown discharge but i woke up today and i was bleeding but my period ended last week. what happened?

Breakthrough bleed: Sounds like breakthrough bleeding which occurs when you have bleeding at unscheduled times while on the pill. Brown is simply old blood that has been sitting at the back of the vagina. Often things get back to normal the next cycle. If not then schedule a visit to discuss changing brands or changing birth control methods. This is very common. Other than being annoying it is not dangerous.

Break through bleedi: It is not uncommon to have break through bleeding while on the pill. This is very common in women taking low dose pills and either skipping a day or taking the pill later in the day from the previous pill.