Bled heavy for 1 day, began having light bleeding for a couple hours then eventually brown discharge. this is my 2nd cycle after plan b. what's wrong?

Plan B: Potential side effects w emergency contraception include menstrual flow changes (spotting, bleeding, early or late period). Take pregnancy test ; notify dr if your period is 7 or > days late. Even though Plan B is out of your system relatively quickly, the hormonal changes that occur may take up to several months after the Plan B was taken to even out.