Re: over one year "sinus" problems... please help!
I have a couple of thoughts for you but also want to clarify a couple of things in your post that seem contradictory. You mention that you have PND every day but also say you have "no nasal discharge". PND is nasal discharge that happens to run down the back of your throat so it would be great if you could clarify what's going on there. Also, you say that you had a CT scan but "no ENT has looked at it" which makes me wonder who ordered the CT scan and why.
To answer a couple of your questions, it's certainly possible that the situation in your sinuses could change A LOT over the course of a year (and dental x-rays aren't a very good source of insight into what's going on inn your sinuses to begin with).
It's also important for you to know that an endoscopic exam by an ENT doesn't show what's going on inside your sinuses but helps the doctor see inflammation and infection that might be draining from them, so the fact that the ENT didn't see anything doesn't necessarily mean that nothing was there (which is why I'm curious why the ENT never looked at the CT scan).
It's also good to keep in mind that 6 days on a steroid spray and sinus rinse isn't enough time to see results so give it some more time.
In general, your symptoms could be allergy related or could even be caused by acid reflux (which can irritate the lining of the sinuses and cause inflammation that leads to PND and infections) so you probably need to find an ENT who really understands how to treat chronic sinusitis to take a look at the CT scan, perform another endoscopic exam and try to help you get to the bottom of what's causing all of your symptoms.
It's unlikely that what you're dealing with is fungal - much more likely to be bacterial (amoxicillin is not a very powerful antibiotic and isn't that effective at treating sinus infections) but there may be some underlying inflammation that is keeping the infection from getting resolved so you may need a course of oral steroids to help get the inflammation under control (followed by ongoing use of the steroid spray and saline irrigation).
You might also want to try an antihistamine like Zyrtec or Claritin (they don't make you drowsy and are available without a prescription) and even an oral decongestant like pseudoephedrine to see if that helps with your current symptoms.