Some good advice already given and I will re-enforce.
Yes, most definitely see a rheumatologist - this is a given for an evaluation of pain medication management and more. You might also have an un-diagnosed - as of yet - autoimmune disorder. And autoimmune disorders can be hard to pin-point. Often it's trial and error. But certainly worth exploring for proper treatments. Re: the movement of your jaw. A TMJ specialist might be a very good idea and TMD (disease) can be cause of your facial/head pain. Also we don't usually think of this but arthritis in the jaw is actually very common. If so, mouth guards are called for to align the jaw - as well as low impact jaw exercises. Osteopenia & low bone density is putting you are on the road to full blown osteoporosis which you want to avoid as best you can. Medications are available to help you avoid the development of osteoporosis. Do you have a treadmill? If so, start walking...of course slowly at first even it's just for 10 minutes to start. Gradually start to increase but gradually. Getting some hand weights - just 1 or 2 pounds, and again, starting very slowly just for a few minutes can be helpful.
The advice to see a personal trainer who specializes with your condition is right on. And a walking program is easy to do...just be consistent with it and sometimes is easily the best exercise.
I understand your feelings of "daunting" to think about making an appointment at a top health facility. I have been there also. It might take time...it took me forever to get an appointment at Johns Hopkins in Baltimore, MD for an evaluation of my relentless migraine condition but once you are an established patient at any top facility - follow up appointment are easy as you are already in their system. That's the trick...getting into their system.
If I were you, I would get into a top facility, you are quite ill and dealing with a lot. The waiting time to get an appointment and their request for a referral and all prior medical evaluations is time consuming but worth it in the long run. So I would start the process with a simple phone call. Even calling top medical facilities in the country could be daunting (been there also) but don't give up. Work on this every day as it will take some time. Northwestern and, of course, the Mayo Clinic/Cleveland Clinic (even better) are the best. An appointment might involve a plane trip. I have been there too but did it. After an initial appointment, all the top medical centers do telemedicine so your first visit is in person...but not the rest if you chose.
As I said, don't give up hope to improve the quality of your life. It is going to take some doing...unfortunately, the name of the medical game these days. Hang in there and start moving in a positive direction to get the best medical help you can. Be organized about it all...as it is a lot to handle but you can do it! The very best of luck to you.