thanx for sharing your concern,
according to the symptoms you are presenting here most probably you are suffering from any of these.
1. stress related ulceration.
2. deficiency of vitamins.
3. allergy to some food products.
4. allergy to any medications.
5. improper oral hygiene
Pain in gums and cheek mucosa indicates inflammation of oral mucous membrane
accumulation of plaque and calculus may lead to gum inflammation
, bacterial or viral infections of the oral mucosa leading to mucositis or fungal infections like candidiasis.
Exact cause can be ruled out only after clinical examination so i suggest to to consult a dentist
and get it confirmed.
Meanwhile you can use antiseptic mouth wash like chlorhexidine
or betadine for mouth rinsing .
Multivitamin supplement and vitamin C lozenges, twice daily helps.
hope this helps.