if you feel safer getting plan b it would be fine, i mean it is just hormones.
if you take your pill the same time each day and have not missed a day, your chances are low of becoming pregnant.
but if you want to be extra sure i dont think that anything bad could come from taking plan b.

and yes im pretty sure that taking cold medicine can mess with bc. so perhaps taking plan b would be a good thing to do.

whenever you have sex you should use a condom, even if you are on the pill, to protect you from a sexual disease-not saying your partner has one- and to make sure you are extra safe.