it might be the dust you should try vaccuuming it ?
I agree it could be that something you are allergic to is on the couch, whether it was cleaned or pet that someone brought over, some perfume someone was wearing etc. If you can get rid of the couch. It might be a good idea to get leather or something you can wipe off easily. In the meantime take some benedryl at night for a few days or go see your doctor to get rid of the rash.
mkh9
Is the furniture new? Did you have it treated with fabric protection? Is there an odor? I am not a health professional, but sold furniture for 20 years. My advice would be either cover it with a throw or have it cleaned to see it that helps.