Common allergens are pollen, mold, dust, pet dander, synthetic fiber, cosmetics or
drugs. You must get an allergy test done, either a skin test or RAST, to know what you are allergic to. It could also be mold allergy due to working in AC environment for long. Consult an allergy specialist.
Meanwhile try deep breathing exercise and steam inhalation. Over the counter antihistamines, decongestants, non steroidal anti inflammatory drugs all help.