A person dear to me has rheumatoid arthritis, and her immunologist and nutritionist told her to avoid nightshades, which contain the toxin solanines, which aggravate arthritis. Check out
http://forum.davidicke.com/archive/index.php/t-160121.html
Since she carefully researched what she can eat, she has not had any more painful flare ups of arthritis. As a bonus, her husband, who joined her in the diet, saw his psoriasis clear up. She mentioned that beside the potatoes, tomatoes, peppers, and eggplant, she finds blueberries and rosemary also cause her trouble. As an aside, black pepper is ok; it is not in the same family as all the other peppers. She has learned to read labels carefully. Beware of "modified food starch" which is often potato starch, "vegetable broth" which often contains tomatoes, and "spices" which can contain paprika and other kinds of pepper.
Once you are in better shape, consider joining a beginner tai chi group. This is a gentle but comprehensive exercise that uses isometric movements to strengthen you and improve your balance. You feel the workout, but it is relatively easy on your body.
Good luck, and I truly hope you feel better. Being able to knit is such a mental health joy. I had years with carpal tunnel issues, and once I retired and had microsurgery by a specialist in hand surgery, my whole life took on a new brightness. Among the other benefits was meeting so many kind and lovely people around the world on KP.