Have you tried allergy shots (immunotherapy)? My Brother had severe sinus symptoms from allergies for years, and he finally went and got allergy shots. He says the shots have helped so much that his fear of needles isn't enough to keep him away from continuing to get the shots.
For my own allergies (sinus also), I find eating any uncooked dairy makes it worse, and also find that regular sinus allergy medications do nothing. My doctor gave me a prescription for Pulmicort (an asthma inhaler) and told me to fit a baby nipple over the top of it to form an adapter for my nose. He said to cut the top part of the baby nipple off and then insert the tip into my nose and use the asthma inhaler by breathing the inhaler medicine up one nostril at a time. This method has worked very well for me. Maybe you could ask your Allergist or ENT about it?
Another thought is that sometimes allergic sinus symptoms are made worse by sinus infections (bacterial, viral, or fungal) that may need to be treated at the same time as the allergies are treated in order for there to be any lasting relief.
Finally, have you tried nasal rinsing with saline (using a netti pot or other similar method)? I've heard of lots of success stories with the rinsing because this method removes a lot of the pollens, dust, etc., that cause the allergic reactions in the nasal passages. My aversion to saline has kept me from trying it so far, but I might bite the bullet and give it a try sometime soon.
Good luck whatever you decide to do,
Gluten & Sulfite Sensitivity, Multiple Food & Inhalant & Medication Allergies, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD (Lupus?), Osteoporosis, Anemia, Very Low Lymphocyte Counts (T-Cells & B-Cells), malabsorption/malnutrition, etc., and now possible Lyme Disease (Igenex Lab says IgM WesternBlot is positive)
Meds: Pulmicort, Injectable Vitamin B12, Herbs, Nutritional Supplements, Essential Oils, Homeopathy.