Has anyone mentioned antibiotics to you? I ended up with pneumonia when a post nasal drip turned into an upper respiratory infection. So I take sinuses very seriously. Having said that, the bad breath part of your deliema sounds more like a stomach type problem.
If I were you I would get to Ear, nose & throat specialist A.S.A.P. Good Luck to you, let us know how you are doing.
I'm sorry I just reread your post, you've already done that! Well I would go back and let him/her know it didn't work. They have many tests to determine what's wrong.