I hav a blister on the upper wall of my mouth. it is happening regularly n stays for a day or 2. why this is happening?

Canker sores: are not pleasant and can be painful and uncomfortable. Canker sore is the most common oral lesions. Individual ulcers typically last 1-2 weeks. The condition is idiopathic (the cause is not known) and recurrent aphthous ulcers are usually self-limiting. Your dentist may prescribe an antimicrobial mouth rinse corticosteroid ointment to control the pain and irritation.