Dust is all over your room, not just your air. Vacuum your mattress. When you vacuum your mattress have someone agitate the mattress by stepping on it or jumping lightly on it, this will release some more of the trapped dust within the mattress. Wash your bedding on a routine basis. Use an allergy mattress cover and duvet/blanket cover. Wipe down areas around your bed on a routine basis such as your headboard. Vacuum the floors and your pc. Never wear your street clothes to bed. Change when you get home. That way you reduce the chance of bringing more allergens into your home. Wash your clothes. Lastly, most ppl are not allergic to dust, they are allergic to the feces of the dust mites that feed off of your skin.