Hi
the retromolar trigone region u are trying to show in the picture seems to be slightly inflamed. It can be due to partially errupted or angulated wisdom teeth (both upper and lower) . If thats the case then u might have to undergo wisdom teeth extraction.
Next Steps
Consult a maxillofacial surgeon
Health Tips
rinse with lukewarm water with a pinch of salt 4-5 times a day , consult a dentist preferably a maxillofacial surgeon at the earliest