I am so sorry that you are having these issues. it can be frustrating to chase a diagnosis.
Let me tell you that there are more than 100 diseases that can mimic MS symptoms, and yes shoghrens is one of them. The positive ANA titer and the rhuemy stuff are strongly leading towards a suspiciion of sjoghrens. Have they done a lip biopsy on you? that is the difinitive test for it.
Some of the other stuff that can "mimic" MS and a positive ANA is lyme, or lupus. Make sure they send your lyme test out to the special lab. more than 75% of the normal labs that routinly screen for it, have false positives in the general population. there is a special screening lab that deals in highly sensitive testing. I would search out Lyme sites and ask their opinions on which lab to send your blood to.
Lupus would also land you in the Rhuemy chair. its a disease that can closely mimic MS including the lesions. It too is another one of those diseases that you get the lable for after loads of ruling out for other stuff. One of the characteristics of Lupus in a redish area on the face/cheeks that can spread across the cheek bones. it can spread across both sides of the face and if you step back from the mirror it would look like the shadow of a butterfly sitting on your face, spanning the bridge of your nose/cheeks. The Lupus.org sites have many good pics of what this looks like.
lastly sjoghrens can be 2ndary to MS. I know because I have it. The primary sx are dry mouth, dry eyes, and dry skin. its funny because I have a moist mouth, but my eyes are dry enough that i needed plugs to prevent any moisture from escaping. My lip biopsy was negative, which means its a 2ndary system in my MS dx. The treatments for Sjoghrens is about the same as for lupus. Steroids! Great oral/mucousal hygiene, and tons of wetting agents, like drops or gels for eyes to keep them protected.
It sounds like you already have a good Rhuemy working on the case. Make sure they test a Vit D and B12 level on you. Those are two things that are easily detected, and easily missed, and easily corrected. Feel better soon.