Is there a way to completely get rid of halitosis?

i have post nasal drip and every time i eat i get terrible TERRIBLE bad breath because of my halitosis. Is there a way to cure this. I brush twice a day, floss, use a mouthwash, chew sugarless gum every day to keep fresh, drink lots of water, and still STINKY BREATH!! oh goodness anyone know how to cure it so that i dont have to use tons of gum to cover up the stench?