What causes the brain fog associated with sjogrens/lupus?

Inflammatory illness: With your history of allergies, plus these inflammatory autoimmune diseases, I'll bet you are sub-clinically hypothyroid, and would benefit from thyroid replacement. For Sjoegren's and Lupus, try Peony glycosides and DHEA, from a health food store. Usually, I start women on 25 mg of DHEA in the AM, but those with Lupus can tolerate higher doses--50- 100 mg. Also, try Afrin nasal spray.

Generalized inflam: inflammation. This occurs in even the mildest autoimmune diseases such as PMR. Verifyable and monitorable with a simple sed rate. Steroids (but not NSAIDS!) ameliorate this effect of inflammation. (you can have direct brain effects by lupus; it is very severe and often stroke like.. but more than 'fog').