Thanks for asking the query,
Bad breath can be because of several reasons,
Poor oral hygiene , deposition of plague and calculus, periodontal infections , tongue coating , xerostomia
, faulty restorations retaining food and bacteria , oral pathologic conditions , mouth breathing habit , use of certain medications fasting , starvation
, foods like garlic , onion
Diseases of GIT, GERD ,Nasal infections like rhinitis ,
Pulmonary infections like bronchitis
Systemic conditions like diabetes
I would suggest you to get a complete checkup done.
Visit to a Dentist
, get complete mouth scaling and polishing done .
mouthwash gargles twice daily .
Drink lots of water.
Maintain a good oral hygiene .
Hope this helps out.