I took plan b and a week later (also a week before my expected period) i had brown discharge that turned bright red for a few days and is brown again?

Plan B: often affects the menstrual cycle, causing withdrawal bleeding earlier than when a period is due. This one of the side effects of the medication. Plan B is intended to be used as an emergency form of birth control. It is not intended for use as a routine form of birth control. Talk with your doctor about the many forms of birth control available.