Could be infected wisdom tooth due to food trapping there. You should get it checked, X-rayed immediately to rule out pus accumulation (abscess). Consult a dentist immediately.
Next Steps
Do warm saline gargles 2-3 times a day.
Go to dentist immediately.
Health Tips
Local abscess around third molar(wisdom tooth) can grow and lead to other problems. please get it checked immediately and if recommended tooth removal, get it done.