If you have mctd that includes polymyositis, an idiopathic inflammatory muscle disease, which produces weakness in your proximal muscles (all those around your hip and shoulder girdles). Weakness and sometimes pain and soreness are common symptoms. My case was so severe that I was completely crippled but most cases are much less severe. Most cases are complicated with a variety of symptoms from any of the 3 diseases ....lupus, scleroderma and polymyositis.
I cannot explain some of your symptoms so you might have something completely different. Lupus is a very strange disease and can cause muscle weakness, swelling and pain. It can also mimic other diseases which is why it can be so difficult to diagnose.
Suggest you write down ALL your symptoms whether you think they are important or not. Also list all your tests if other doctors have been involved. You might consider going to a hospital clinic like Mayos, Cleveland Clinic, Johns Hopkins.... They will try and diagnose you with a team rather than just one specialist.
Disability is tough to get and you need a diagnosis to qualify. I got it but it took 3 tries.
Sounds like you are seeing the right doctor if you have an auto immune disease.
MCTD (lupus, scleroderma, polymyositis). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, Barretts esophagus, quadriplegic in 2005. Recovered and now active in skiing, tai, chi, hiking, golf. Meds: prednisone 2.5mg, imuran 25mg, amlodipine, benazapril, omeprazole, potassium, folic acid, vitamins, maxide and various supplements and vitamins.
Remain optimistic and you can overcome the odds.