Don't stress! This is not abnormal. Breakthrough bleeding (anything from light brown discharge up to bleeding like your regular period) is the most common side effect for women beginning birth control. Just continue using your birth control as normal and give your body time to adjust to the birth control you are using.
https://www.nurx.com/faq/i-have-bleeding-during-my-active-birth-control-pills-is-this-normal/