Hello and welcome to hcm forum,
The pain can be due to the root canal
treated teeth which has re-infected.
I would advice you to get a thorough clinical and x-ray evaluation done.
If required,the rc-treated tooth has to be extracted.
Take complete course of antibiotics too.
Maintain oral hygiene
Apply intermittent hot and cold
packs on the affected site.
Avoid mouth opening too widely.
Jaws has to be immobilized for a while.
Use warm saline and betadine