I have a bubble like blister on my top gum between my second and third teeth. I have had this before, but seems it went away on it's own. i've noticed this one for about 2 weeks now and it appears to be bigger. It does not hurt, but I can't stop rubbing it with my tongue, which can make it a little sore. It's a clearish white color. Could this be something serious, and do you have any idea what it could be? i'm starting to get concerned.

Thanks you.
Denise