I pretty much had the same problem in both sides of my head. When sinusitis goes on that long you get bacterial, viral, and fungal infections all mixed up in one. Since you've gone to the doctors and exhausted every other avenue, (which I also did), I will now recommend the technique that will work. It's the Flip-Turn Sinus Flush. It's mildly risky, because you have to bend over, preferably in a shower, but it's also possible to do in a bathing suit outside in some grass to be safe.
Regular sinus irrigation is useless in your instance, because gravity shoves the saline out before it reaches the infection. Bending over uses gravity to your advantage. The journal will explain why antibiotics didn't work in your instance, and why washing the infection out does work.