Hi, the primary cause of bad breath is inflammation in the gums, which is caused by plaque and calculus, get scaling and polishing done, most probably your problem will be solved. Secondly you should clean your toungue. And lastly your general health is associated with bad breath too.
Hi.. .it's really unfortunate that you are suffering from Bad Breadth.... in medical terminology...its called Halitosis.
There are multiple reasons for your bad Breadth. To cite a few.... it could be due to presence of some local factors like.... poor oral hygiene, Dental Caries(cavities), etc.
Systemic causes include...diabetes, indigestion/constipation leading to acidity and fishy odour, insufficient water intake, starving for long periods...etc.
Advise you to first consult your Dentist and eliminate local factors, if any, before consulting a physician.
Hope this answers your query.