Yeah that's a tricky road to navigate. Hopefully in time you'll get to see a good Rheumatologist or similar to figure out or at least rule out some real deal inflammatory disease that might be affecting you. I have a Rheumatologist specialist now due to my primary doctor thinking I had something like that going on.. the one thing I've learned from all this is that so much of this stuff is tons of blood tests and guesswork that just takes a while. In the end she ruled out most of those diseases (& realistically I didn't present a lot of symptoms) but in my case there's a some sort of early onset bone density issue and arthritis so it's just something to monitor and keep tabs on.

If you're luck(ier) maybe there's just foods you need to avoid due to reactions (allergy, inflammation, whatever). I know someone who has a very restricted diet, she was just constantly getting sick with random symptoms most of her life until she finally saw a specialist and got tested for different foods and ingredients that affect her.

The long COVID effects could actually be a ton of other things. Before COVID was a thing there wasn't really a name for that but those same symptoms are often experienced by people who were infected/recovered from other viral infections. Like for example the type that get carried around by mosquitoes. A family member of mine was infected and recovered from West Nile Virus - I only say "recovered" being that the hospital discharged him once he was well enough so statistically he "survived" WNV. But he has random symptoms that stuck around afterwards. A few went away after a year or two, some stuck around for longer.. it's all the same long COVID stuff that doctors just sort of shrug and say that the tests look normal.

Over time if you manage to get through all the different specialists and tests some of those things will become clearer. And don't be afraid to try seeing new doctors / specialists if the ones you're seeing aren't really doing much to help you.