Get the IOPA X-ray of the affected area and it will give the clear picture as what is the reason. Sometime the dental caries exposes pulp which causes a peri apical abscess which is usually characterised by swelling of gingiva adjacent to that teeth.There may also be the sinus tract.
The interpretation of IOPA X-ray will guide about the correct treatment plan.
Next Steps
You can take :-
Tab Flemiclav 625 mg twice daily after meals for 3 days
Tab Zerodol SP twice daily after meals
Cap Becozinc once daily after meals.
Health Tips
Do warm saline mouth rinses twice daily.