Not sure if you have been tested for allergies or not, but what you explain sounds alot like what my son went through. He was allergic to many things, esp dust mites and animal fur. He received approximately 4 yrs of allergy shots, and was on a low dose of antibiotics for a year. The antibiotics seemed to do the trick. We now have 5 dogs and I don't remember the last time he had a sinus infection. Hope this helps, good luck.