Took the planb pill , a week after taking it i have a light brown & redish discharge , could i be pregnant ?

Yes: Yes, you could be pregnant. Consider taking a home pregnancy test. If it's negative, then consider repeat in 5-7 days. Taking Plan B can alter your normal cycle so it may not be clear for another whole cycle when you are going to ovulate and have a menstrual bleed. In the meantime, continue to use a reliable form of birth control. Best of luck.