Bad breath or halitosis can be due to many reasons. Make sure your dental hygiene is proper, visit a dentist for checkup, there may be a hidden cavity or plaque.
It can be due to post nasal drip, a condition when nasal secretions flow back into throat.
Other possible cause of bad breath can be smoking, tobacco chewing or alcohol intake. Dry mouth can also cause bad breath,keep your self well hydrated, drink plenty of water. Certain food like meat and egg can cause bad breath make sure to brush your teeth after consuming them.
You can prevent bad breath by flossing your teeth, eating vegetables and fruits. Eating smaller meat portion. Drinking plenty of water and keeping your teeth clean.