I have a fever blister inside my mouth , bought numerous stuff from the pharmacy , but nothing helps. what can i do to get rid of it?

Mucocele?: Fever blisters (oral herpes) do not occur inside the mouth. And any blister lasting more than a day or two is not herpes, especially if painless. Most likely a mucocele, which is harmless and results from temporary blockage of a mucus gland duct. Small ones usually can be safely and painlessly pricked with a needle and do not recur. If large or repeated, see a doctor. Google mucocele for more info