Bad breath can usually be cured. Bad breath can be caused by food rotting in the mouth, stomach acid regurgitating up to the mouth and infections releasing chemicals that smell. Your doctor should look for white dots on your tonsils, that are often pieces of food that your saliva has turned white. You can remove them by gargling after every meal or by rubbing a Q tip against your tonsils.

If you have belching and burning in your chest or abdomen, you may have acid backing up from your stomach (1,2). Your doctor can order a blood test for helicobacter, the germ that causes stomach ulcers. If it is positive, you can often be cured by taking antibiotics (metronidazole or clarithromycin with omeperazole) for one week.

Another cause is an infection in your mouth, teeth, gums, throat or esophagus. Your dentist should look for an infection and order a throat culture. If it grows out bacteria that cause disease, your doctor can cure you by prescribing the appropriate antibiotic.

However, more than 30% of the time, the cultures do not grow out a bad germ (3), and you still should be treated with antibiotics. There are so many different germs in your mouth that it is impossible to tell whether a germ that is found there is causing the odor or is a normal inhabitant of your mouth. A 5 mg pilocarpine pill before each meal, or chewing gum, can increase saliva and help wash down food before it is fermented in your mouth

See references here.