Little Lotus, I’m guessing fasting won’t make much of a difference. If anything I’d think a few days off of eating processed starches and sugars would be good. I get cold sores a few times a year, usually when I’m stressed (dealing with my unstable mother is a HUGE trigger) or have hormone issues. They’re such a pain in the you-know-what.
If you want to shorten duration, I’ve used two things that seem to help a bit (cut it down to a few days vs a whole week) Oregano Oil, which supposedly has some strong anti-viral properties. This stuff stings like heck when you put it on (and it tastes horrible!!), but a few drops applied right when you start noticing the cold sore help. I apply it twice a day for the first two or three days. The brand I’m using now is P73 Oreganol but before that I just some little gel caplets that I’d pierce and squeeze on to the sore. I’ve also used ozonated sunflower oil. This stuff is pretty cool and has a lot of uses for different skin ailments (it’s like magic on my daughters eczema). I don’t know your location so I don’t know if you’d even have access to these supplements (they’re easy to purchase online in the US).
good luck…I seriously feel your pain. 🙂