I am not familiar with your diet. A couple of years back I had symptoms that pretty accurately mimicked lupus. My problem was more the the heart, though. This caused massive fluid retention, which in the end started to affect my kidneys since lasix would not work. At the same time I also experienced severe binge attacks that were further fueled by my cycle. I found out over time that my inflammation was significantly enhanced by my diet that was high in carbs. By eliminating most sources of carbs I was able to reduce inflammation and eliminate fluid retention. I also found that a low carb diet significantly reduced my desire to binge. Since I did not suffer from autoimmune disease in the end, I do not know whether carbs affect lupus symptoms. But you may be able to do some research and it may help reduce steroid use or steroid hunger.
As far as I know, it is not entirely clear how prednison works. But there may be an interaction with several hormones including estrogen. I found that my hunger binges were fueled by several factors, including carbs, estrogen and probably borderline levels of adrenal and thyroid hormones. All of that combined into a vicious cycle. Balancing everything and taking additional supplements including vitamin D helped. Also make sure you sleep enough and go to bed before midnight.
I would work with your doctor and do research into nutritional and hormonal factors that influence autoimmune disease. I do not think it is an accident that lupus affects predominantly women and hits when hormones are likely to go off balance. Importantly, unbalanced hormones, particularly when combined with insulin, also cause binges and weight gain in women.
Finally - and it is at present unclear what it means - autoimmune symptoms (and prednisone action) may be influenced by hormonal factors other than we normally think about. There is some interesting research going on regarding the role of gut bacteria in autoimmune disease:
http://www.ncbi.nlm.nih.gov/pubmed/23328391
http://www.ncbi.nlm.nih.gov/pubmed/18806780
Changing your diet or taking prednison may alter the composition of these bacteria. But this is just a hypothesis at the moment.