Thanks for writing to us.
Regarding the painful swelling in the oral cavity, it could be mucositis
or inflammation of the buccal mucosa secondary to vitamin deficiency
or allergy to some food/medicines. This will require a thorough examination of the oral cavity and throat as well as blood investigations to rule out anemia.
If you can mail me a photograph of the oral cavity, I will be able to help you in a better way.
For the time being you can try the following measures which will give you some relief:
1. Drink plenty of warm water; avoid hot/cold food and beverages.
2. Avoid fizzy drinks, alcohol and smoking if any.
3. Try taking mild anti-inflammatory medicines such as diclofenac
for the pain relief and multivitamins for increasing the body immunity.
4. Also, you can try taking short course of oral steroids such as prednisolone
for a quick relief.
Hope this information helps you.
Wishing you good health...