Thanks for your query, I have gone through your query.
The possible causes for the bad breath could be the dry mouth(in your case) the gum infection or deposits, pus discharge. Consult a oral physician and take a opinion to rule out these causes. these causes can be treated by getting your teeth cleaned and maintaining oral hygiene. Consume lot of water and keep the oral cavity clean.
If these causes are not there then, it can be secondary to respiratory disorders like sinusitis or gastrointestinal disorders. Consult a ENT and Gastroenterologist to rule out these causes.
I hope my answer will help you, take care.

hellooo...read thru ur query...first of all i wanted to say is to be cool...halitosis is something which most of the people has ....some mask it by using certain techniques...some become sad and tensed..actually sad and tension causes dryness of mouth and it leads to halitosis... as u said u follow evrything usually a dentist tells to reduce halitosis and urs not reducing i suggest u to use chewing gum regularly(sweetless can be done as it may not cause decay too)so that ur mouth wont get dry...drink water regularly..if possible keep ur mouth wet...dont skip breakfast lunch or dinner as if ur hungry u may have halitosis caused from gastric tract...check for sinusitis...if ur taking any other medication it can result in dry mouth and halitosis....if after following these still persists meet a general physician check for systemic diseases as it may be the cause...so cheer up..be cool...hope ur benefitted something from this reply..have a healthy day!!