I have a white painful"sore"inside my mouth in the very back of mouth.kinda beside uvula.very painful, has grown a lot since this morning. ?wat is this

May be viral: The blister might be viral. If it is a shallow yellow white ulcer with red rim then probable aphthous ulcer which is from inflammation of the mouth lining and will resolve in 7-10 days. Steroid cream applied to the area, cepacol lozenges, an Aspirin dissolved in water then gargled might help.

See below: Have a clinical examination by an ENT for a definitive diagnosis. Good luck.