I would try the nasal spray but also see another ENT or possibly an allergist. Sometimes really bad allergies can present symptoms of sinusitis, but you don't truely have an infection. And as you've discovered, most ENT's act like you're wasting their time if you don't have an infection.
As far as nosesprays go, make sure you use a saline spray and blow your nose first before using it it. My allergist actually had me irrigate before using it it. Otherwise, in his words, "you're putting oil on water." The spray just sits on top of the mucus, and never reaches your nasal tissues where it needs to go in order to work.