Most likely the underlying cause is Periodontal disease.Are you suffering from
Diabetes or taking any medication ?
Adv - 1) Proper twice daily brushing
2)Interdependent cleaning (floss, interdental brushes)
3) Tongue cleaning (very important for halitosis)
Some investigation are required like 1) OPG X ray
2) Hb a1c test
Next Steps
Next go to dentist for professional cleaning (scaling, polishing & root planing)
Health Tips
Chlorhexidine mouthwash wash (.2%) twice daily for 1 week