Most cold sores are a type of herpes
(not the same type usually that causes genital lesions) and if caught early (ie when the area starts to tingle or burn) can be suppressed with an antiviral
medication like Famvir
) or acyclovir
If you can't get a script for one of these meds, try applying ice to the area 4-5 times a day as this will inhibit viral replication and speed healing.