I thoroughly recommend you try virgin coconut oil. I have used it on my own cold-sores and was amazed at how well it works. It zapped the cold-sore before it even had a chance to form.
Coconut oil attacks lipid-coated viruses such as the herpes virus (both type 1 and type 2).
My advice is to apply it topically the first sign of trouble. If you want extra protection try taking it orally.