Plan B Question

I ran into some issues with my birth control and for that reason I'm off the pill for a month. We've been using condoms and have tried to be careful. There was a mishap a week or two ago and I took Plan B the next day. We had another problem where the condom spilled as he was pulling out today. I'm wondering if I can take Plan B again tomorrow or is there any problem with taking it twice before my period. I've just read somewhere that it doesn't work if you've already taken it once before your cycle.