Took plan b three weeks ago,on the day my period was due, i just got some light spotting for two days,is that a sign of pregnancy ?

Maybe not, but...: Taking Plan B (or any other emergency contraceptive pill) can alter the timing and quality of the current cycle's menstrual bleeding and of the upcoming cycle. One should check a home urine pregnancy 3 weeks after taking Plan B, to make sure one is not pregnant. Also, if having sex, one should be sure to use good contraception all the time, so that Plan B is not needed in the future.