My thoughts on the excessive yawning is that you may want to consider asking your physician if you should have a sleep study test done. I know in fibro & CFS patients, we have some degree of sleep dysfunction.
If you haven't been tested for lyme disease yet, I would strongly recommend discussing this with your physician. I can tell you that I'm thinking so far that your symptoms could be due to fibromyalgia and / or lyme. But there should be many tests that need to be ruled out first. It sounds like they ruled out Sjogren's Syndrome and probably already ordered an ANA on you. An ANA test could help rule an autoimmune issue.
I hope your physicians also checked your thyroid. One thing I can tell you is that many fibro & CFS patients have a low thyroid, but the standard thyroid tests fail to pick that up. Here's the info:
T3 REVERSE -- "The mix of treatments needed varies from patient to patient. There are some abnormalities that are common. For instance, close to 100% of individuals with these syndromes have low thyroid. This is, however, usually not picked up on the standard blood tests because the TSH is not elevated in these individuals due to pituitary dysfunction. Many of these individuals will also have high levels of the anti-thyroid reverse T3, which is usually not measured on standard blood tests. In addition, the majority of individuals can also have a thyroid receptor resistance that is not detected on the blood tests. Consequently, thyroid treatment, especially with timed release T3, is effective for many patients. T4 preparations (inactive thyroid) such as Synthroid and Levoxyl do not work well for these conditions."
Kent Holtorf, M.D. --- link to article: http://www.immunesupport.com/fibromyalgia-treatment.htm
And burning sensations in fibro patients: