This article might help you understand brain fog more but I don't know of any way to treat it other than the treatments normally given for lupus. I have cognitive impairment (short term memory, concentration, and coping in general) and at first did not want to recognize it was happening. Although I am retired I do some computer/network consulting which is very detail oriented and have to make sure I am prepared. I write down everything and do not rely on memory for anything. Reasoning ability is good but the memory banks are definitely damaged...most noticeably short term but also long term to some degree. Over the past 6 years in remission it has improved somewhat but not anywhere near 100%.
http://thelupusmagazine.blogspot.com/2010/08/kim-nault-lupus-brain-fog-lupus.html
Have considered taking some college courses and decided not to do it due to memory and difficulty concentrating when reading. As a grad student you do not have that option. The best I can offer is that I have adapted by organizing myself and never relying on memory. Life is good but not the same.
Bill