My friend was diagnosed with lyme disease in his mid-20s after years of symptoms similar to your own (brain fog, extreme fatigue, etc.). The hard thing is that even lyme disease itself is a constellation of illnesses, he had to work with mulitple specialists for years to confirm what the issue was and get the proper treatment.

In his case, he is mostly back to normal, albeit gluten intolerant, which will cause his symptoms to redevelop, namely spinal inflammation.

Its hard not to engender helplessness when hearing or dealing with types of issues, but I wish you perserverance in your search for answers, and grace when dealing with your problems.