I had a very bad cold sore a few weeks ago, it spread and I ended up with a couple. I actually tried four different things on my cold sores, what you use is completely up to you but sadly these things take a week or two to disappear but any swelling should go down in a few days.
I actually used blistex on my cold sore to begin withm I found it very useless and when the tube was finished, I decided not to buy it again.
I then went on to use good old zovirax which actually made my lips worse for some reason, used it plenty of times and never had that problem before.
I was left without cream for about two days so used a little bit of tea tree oil on my cold sore. It's very painful, it tastes disgusting and you smell rather horrible but it helped with the pain side of my cold sore which was good.
After trying all those things, I actually went to the chemist and the woman recommended me Aciclovir, which is pretty much the same as Zovirax. I found that really helped with the cold sores that I had left and I personally will be using that from now on.
Best thing to do is use Zovirax or Aciclovir, very similar apparently and probably two of the best creams for cold sores. You could also just nip into your local chemist and they will show you the products which the have and probably recommend something. Just be careful with your cold sore, no kissing, oral sex and don't share glasses/bottles with other people. Make sure your hands are always clean, wash them before and after you apply any cream to them so that it doesn't spread!