Okay, first of all, why are you taking Plan B when you've had protected sex? For the most part, condoms work if used correctly and if they don't break.
Plan B shouldn't be used regularly, as a routine form of birth control. Read the info in the following link:
http://www.drugs.com/plan-b.html
I would recommend talking to your doctor about alternative forms of birth control if you're concerned about condoms not being sufficient (which is a reasonable worry).
Good luck to you!
I believe it's as effective as taking it the first time. The only sucky part about plan B is it makes your period irregular. My sister has taken it a few times & it's barely returning to normal. But hey, there's no baby so it is pretty effective.. if you followed the instructions correctly.