There's no easy answer to your question.
Fungal sinusitis is an issue/question that has caused a lot of discussion in the ENT community over the last 8 years. In 1999 a group of researchers at the Mayo Clinic found evidence of fungus in the sinuses of 96% of the people with chronic sinusitis that they tested but they found that almost as many people without chronic sinusitis showed evidence of fungus in their sinuses.
The researchers hypothesized that fungal sinusitis is much more common than anyone thought. As their results were refined it seemed more likely that it wasn't just the presence of fungus that led to chronic sinusitis (since it was present in people with and without the disease), but the way some people's bodies react to the presence of fungus (specifically the release of cells called eosinophils that attack the fungus and, in the process, cause inflammation in the lining of the sinuses, which leads to chronic sinusitis.
Today there are 3 kinds of fungal sinusitis that are commonly recognized. The first two, Invasive Fungal Sinusitis (which typically affects people whose immune systems have been compromised) and Fungus Balls (which typically involves thick balls of fungus-filled mucus that have to be removed surgically) are fairly rare and would typically have been easily identified by the doctors who performed your surgery.
The third, Allergic Fungal Sinusitis (or Eosinophilic Fungal Sinusitis) is more common but there is no single test for it. Doctors look for a combination of symptoms, including: Positive skin test for mold/fungus allergy, The presence of nasal polyps, The presence of eosinophils in mucus secretions, and a positive culture showing fungus in your sinuses.
Patients with Allergic Fungal Sinusitis are being treated with an irrigation solution of Amphotericin B (an antifungal medication) in addition to the normal treatment regimen for chronic sinusitis. Amphotericin B can be very toxic when taken internally but it doesn't have the toxic side effects when used topically, and has shown promise in some patients with Allergic Fungal Sinusitis.
So, back to your initial question, if you have: A positive skin test for mold/fungus allergy, Nasal polyps, The presence of eosinophils in mucus secretions, and a positive culture showing fungus in your sinuses, you may well have fungal sinusitis and should ask your doctor about trying irrigation with Amphotericin B to see if it helps.
In addition to that (and the shots, daily antihistamine/Nasonex you're already using), you should be on a sinusitis management regimen that includes daily saline irrigation with a SinusRinse bottle, neti pot or other irrigation method. You might also ask your doctor about Singulair or another leukotriene inhibitor - they seem to help with the inflammation, particularly if you've ever had nasal polyps. You also don't mention if they've had you on short courses of oral prednisone which can help reduce the swelling and get your sinuses functioning normally again.
One final thought for you on antibiotic resistance. People don't become antibiotic resistant, bacteria do. As long as you're taking the medications correctly you may never encounter a bacteria that is antibiotic resistant, and getting your sinusitis sorted out will go a long way toward keeping the antibiotics to a minimum.