Hi..
Welcome to HEALTHCARE MAGIC..
As per your complain the symptoms seems to be due to causes like Apthous
stomatitis or Canker sores, viral infection causing Herpetic cold sores while can also be due to
Bullous Pemphigoid..
Consult an Oral Physician and get evaluated..
In case of Canker sores you can be advised to start gargling with warm saline solution.
Gargle with a numbing mouthwash containing Lignocaine..
Take a Vitamin B complex daily..
You can take anti inflammatory painkiller like
Ibuprofen..
Avoid spicy and hard foods..
Take a soft and bland diet..
You can also suck ice and do cool water rinses..
In case of viral infection
antiviral medication like
Acyclovir, Valacyclovir etc can be advised..
Hope this helps..
Regards..