First, I am curious as to what your ENT said. He can scope up there and take a peek right in his office. It's a bit wierd, but not too uncomfortable to go through. You may have nasal polyps or a deviated septum. If he didn't look up there, go find a different doc.
The reason for your bad breath is usually from what are commonly known as 'tonsil stones'. It's the crud that crystallizes from your drainage. They are pretty gross, but go away if you get your tonsils out. This helped me.
Next, make sure you use the neti-pot or neil-med twice a day. it sucks, but over time does A LOT. Trust the product. It really helps. Also, if you get to your doc saying you want to give a strong push to get rid of it, have him prescribe you some prednisone (TAKE IT LIKE YOU'RE SUPPOSED TO). Also, ask for a trial of fluticasone (it's nasal steroid spray that will help all the swollen tissue shrink to open up space for drainage. The steroids suck and you'll eat like crazy for the 10 days you're on it. While you're on it, do the rinses twice a day, nasal spray, and take your Allegra D too. Remember to drink a lot of water so the mucous is thin enough to drain. Often times people don't drain well because they're pretty dehydrated. If you do all this and still have problems, it's time for a CT scan. You're probably 80-90% blocked up there and it'll just get worse.
I had very positive experience with the FESS surgery. (I have to have it every 5 years) It's like a roto-rooting. They don't break any bones, it's outpatient (go home the same day), and honestly, I didn't have pain after at all as there are no pain receptors in your sinuses. So, all in all, focus on the ENT doc and if he hasn't looked up there, get a different one.