I took the plan b morning after pill and one week later in experiencing brown discharge. is that normal or am i possibly pregnant?

Yes and yes: Plan B is at best 75% effective, so also consider pregnancy as a possibility and don't use plan B as you only form of birth control. However, plan B use also typically causes some irregular bleeding like what you are describing.

Can cause bleeding: But, pregnancy is also a possibility as Plan B won't abort a fertilized egg or an embryo. Do a pregnancy test and if negative repeat it in 1 week. If significant vaginal bleeding or pain develop go to the ER because a miscarriage or tubal pregnancy are also possible.