The condition of bad breath is called as halitosis. It is present in your case for 8 years; have you consulted doctor for this in past?
There are many causes for Halitosis.
1] Poor oral hygiene
(not brushing and flossing properly)
2] Gum disease : poorly fitting dental appliances, yeast infections
of the mouth, and dental caries
3] Eating certain foods like onions or garlic
4] Tobacco and alcohol products
5] Dry mouth (caused by certain medications, medical disorders and by decreased saliva flow during sleep hence the term "morning breath")
6] Systemic diseases such as cancer, diabetes, liver and kidney disorders.
Cancers and metabolic disorders, can cause a distinctive breath odor as a result of chemicals they produce.
Diabetes and kidney or liver failure
can lead to a fishy smell.
can also cause a fruity breath odor from chemicals called ketones.
Chronic reflux of stomach acids (gastroesophageal reflux disease
, or GERD) has been associated with bad breath.
In addition, some medications — such as those used to treat high blood pressure
, psychiatric conditions, or urinary problems — can indirectly produce bad breath by contributing to dry mouth.
So consult your doctor to find out in which category do you fit in and get treated.