Had unprotected 2 weeks ago. took plan b next day. 14 days later, today, light brown discharge with some blood. can this be normal?

Yes, but . . .: Plan B is emergency hormonal contraception (birth control). As such, it can/will throw off your menses (http://www.planbonestep.com/side-effects.aspx). However, engaging in unprotected sex also exposes you to sexually transmitted diseases/infections. Whether your light brown discharge represents normal side effect of Plan B or an STD is unknown to me. Only way to find out is to see your Family Doc