I Have Had Chronic Hives For 27 Years. It Has

I have had chronic hives for 27 years. It has gotten much worse during the last seven years and I've had to resort to high doses of steroids and high doses of many antihistamines. They have not found an immune problem, but I do have severe pollen, dust, and food allergies. I would like to get off the steroids especially. I've been to the Mayo Clinic, and they suggested allergy desensitization shots. I also get Xolair shots. Any ideas on how to improve this situation?