My advice is to keep a food diary so you can look back for any correlations between certain foods and bad days. Also a neurologist told me aspartame will magnify pain you already have. Do a healthy doctor approved cleanse and then stick with natural and not processed foods. Also swimming is usually good for inflammation. It's exercise without body weight on joints.
Without a diagnosis, it's just trial and error until you find what works.
I'm in a similar boat. I have pain in every joint and muscle. I have extreme exhaustion, severe brain fog and I'm losing muscle. A neurologist sent me to a fibromyalgia doc. The fibro doc didn't think it was fibro but suspected MS. Brain scans have found no sign of MS. Sleep study diagnosis was Narcolepsy with cataplexy. But that isn't progressive and not pain causing, but I'm steadily getting weaker and hurting more. 15 years ago I did a full body off frame restoration on a car. Now my DRL mod on this Versa is still in the package. All I have to do is run an ignition +12V to the module. This heat takes what little strength I have in a few minutes. I've had my heart checked with echo and stress test and they say it's fine.