im assuming the plan b pill is the same as the morning after pill? f so, my girl has taken it twice. nothing really different. no side effects, but it will obviously effect different people different ways.
honestly, i wouldnt worry about it. out of a full month, the egg only has 2 days to be fertilized //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif. your chances are low for you to be in that time frame, and even if you are, the morning after pill should take care of it.