See, bad breath could be due to many reasons like local or systemic. It could be due to calculus deposit superficial or deep. So for proper diagnosis proper evaluation of oral cavity is required.
Next Steps
Consult doctor online or offline.
You may need deep cleaning of tooth.
Try to maintain good oral hygiene by brushing twice a day, change you brush more frequently, use mouthwash, rinse oral cavity rigorously whenever you eat something, warm saline water rinses two to three times a day.