Tendonitis is an overuse injury, and is usually only stays in one or two joints. When it jumps around without any warning, it's more systemic. I'm in physical therapy, and I also have lupus. I thought it was tendonitis when it first showed up in my elbow, then it jumped to other joints. It may not be lupus, but there are other disorders that have similar symptoms such as lyme's disease, or fibromyalgia. Hope this helps.