There's a website called Victoria's health sorry don't have the address, but they do a product in a small orange tin called Prid. It draws out all of these nasties but you have to put it on and cover it with a plaster. It's good stuff but doesn't solve your immediate problem. You could go with the really hot water on a cloth, or else dab it with something to dry it out. Toothpaste can be quite good as well as the other suggestions here. But if you're run down you might need to boost your immune system, try echinacea for a wee while, or some zinc - be warned though they both taste foul - just try them for a few weeks. Zovirax works best for cold sores, or Boots own version.