Wow, I can relate to much of your post. In the interest of saving time, I'll address a couple of things that really spoke to me.

Neck & shoulder pain, trouble sitting, trouble sleeping. For me, these issues were fibromyalgia. I have muscle spasms in my neck, shoulders & back. Sometimes just turning my head to look at something will trigger it. Constant pain, 24/7/over 10 years. Sleeping was terrible as I often had spasms in my sleep and would hardly be able to love to get out of bed. I fortunately came down with a terrible sinus infection that made me have to sleep sitting up or risk coughing my head off. I discovered that my neck & shoulders were better then, so I bought a wedge pillow and now sleep sitting up. Best thing ever! As for sitting, if there is no back or the back is too ridged (think church pew), I absolutely can't sit. Back pain, leg pain, it all happens when sitting like that.

The eyes. For several months my optometrist and opthalmologist assured me my eyes were perfectly healthy but no one could explain the lack of acuity that was not correctable in my right eye, or the peripheral double vision, or the painful eye movements. The eyes WERE healthy and the problem was with the muscles. Go see a neuro-opthalmologist. That was the doctor that got to the bottom of my eye issues and dxd me with MG.

Keep up with the thyroid issue & take Stellatum's advice, go to an endocronologist! My boyfriend had tons of health issues, turned out to be his thyroid. He was rare that he has both Graves disease and Hashimotos. He had it ablated and now takes synthroid and finally feels better than he has in years.