I had intercourse 5 days ago before my ovulation and took plan b a hour later, its the day after my ovulation and i am having brown discharge?

Plan B is about 95% effective in preventing pregnancy. Plan B does disturb the hormonal status and the brown discharge is likely due to fall in hormone levels. Use contraception all the time, every time, if you wish to prevent pregnancy. You may consider IUD or implanted contraceptive. If you miss your period by 4-5 days, do a home pregnancy test.