Interesting you bring up Celiac Disease, as I found it doing some GoogleMD^tm myself, but had forgotten about pursuing it.
I’m a bit older than OP, but have almost all the same symptoms, and have gotten the same “your just getting old” response from everyone. I still believe mine is tied back to me getting COVID (only tested positive that once), and have hurt basically non-stop to some degree since. I know people have all sorts of long-COVID things from taste, smells, breathing, diabetes, heart issues (blood clots/blood pressure/etc.) and on and on. This woman at work had this wild autoimmune thing with kinda painful rash blots that would randomly popup all over her body not long after she had COVID. I guess it’s possible maybe it triggered Celiac Disease for me.