I am so sorry you are not getting answers. It is very frustrating to seek help and find no relief and no explanation.
Where I live, about an hour from me, is a doctor that is rather unusual but specialized in differential diagnosis. She works in a large compound of her own in the middle of nowhere and all she does is diagnose & then recommend your options. She takes patients only on a retainer and last I knew it was pretty high, like $5000 USD. I have to think she cannot be the only gifted diagnostician out there. I found her asking around in the alternative medicine community about medical doctors that others knew of that might be of help. She is not alternative. She is simply someone who is not within the normal scope of who I might get referred to as she isn't covered by insurance. She didn't just take my money to see me and then charge me a ton more. The retainer covered a lot of things, labs, tests, visits, etc. I believe I saw her about a dozen times (all covered) and she spent 3 hours with me on intake, just asking questions, checking me over, etc. Getting a differential diagnosis the way she does it was nothing like I have ever had before or since. She was absolutely highly involved in time spent with me, with labs onsite and equipment to sometimes get results while I was there. Her recommendations that follow are also pretty different, including dietary recommendations, vitamins, supplements, exercises, the whole thing, on top of any prescribed treatments. And once you are diagnosed, you are done. She is on to other people needing help and you are back to your main care physician with huge folder of test results & documented conclusions.
I tried looking a little online to see if I could find some terminology for you that might assist locating a physician like this, but I am not sure that is the right way. I suggested you asking around as I am not sure I would have ever found her any other way. I will say too that if you suffer, do not give up. There is always a chance they will find an answer and finding your relief is worth that fight.