What Causes Constant Itching In Arms While On Medication For Hypertension?

I am having uncontrollable itching of my arms. Started last year. Just around the middle of my arms. Now my whole arm, one at a time. I have tried Zyrtec, benadryl, cortizone cream and Sarna lotion. The doctor thinks it could pos be an allergic reaction. No allergy symptoms except itching. Now I am on oral steroids. No help. I have been taking 25mg of hctz x 10 years for htn. Any chance I have developed a sensitivity to sulfa