I have alot of the same symptoms and was checked for Sjogren's and alot of other stuff by my endocrinologist I see for my thyroid problem. I didn't have any of the diseases but my potassium, calcium, sodium are all low and had a 24 hour urine done where it showed massive potassium loss which the kidney dr. said can cause the muscle weakness. He said it was a syndrome similar to Gitelman's. I'm on meds now and hopefully it will work. I have a sister with fibromyalgia and I think I have it to. Lots of tender spots and feel fatigued all the time but I'm wondering if it's just the low potassium because it plays a big role along with calcium in muscle contraction and relaxation. You might ask your doctor for a specific Sjogrens test and get a test to check all your minerals. Good luck.