Please get your
thyroid function checked. It could also be due to overuse of AC and heaters. Some fresh air every day with lots of fluids should help.
Generalized itching can be due to allergy. Common allergens are pollen, mold, dust, pet dander, synthetic fiber, food, cosmetics (powders, soaps, shampoos—see if anything was recently changed) or drugs. You must get an allergy test done, either a skin test or RAST, to know what you are allergic to.