Please help. i have this a blister inside my mouth, below on the floor, just below the jaw(teeth). the blister is not sore, and has been there for a week now ?

Blister in the gum..: Just as one can have 'Fever Blisters' outside the mouth, on the lips for example, one can also have it inside the mouth.But there are other causes of blister in the gum inside the mouth. If persisting see Doctor for Physical evaluation or maybe see the Dentist especially if there is some toothache with it.

Oral Lesion: It is very hard to diagnose these issues without a visualization and possibly radiographs of the teeth in that area. No pain does not equal no problem. Any lesion that does not resolve on its own within 14 days should be examined.

Blister: There are different kinds of oral lesions, with different causes, that can be misidentified as a "blister." Must be examined to be properly identified, and then properly treated. Should resolve on its own. If still present 14 days from onset, even partially, imperative that you see a General Dentist or a Oral Surgeon.