I went to a few MDs as well, for what presented like de quervain's tenosynovitis. It was only in my right hand, thankfully, so I could still mouse with my left. I also could use nothing but a split keyboard, which made it tough to use a laptop. And I could no longer use my phone with my right hand either. But after a while, I started getting symptoms in my left as well.
Obviously, no where near as bad as your case, but there nonetheless, for years. MD after MD told me there was nothing wrong with my hand, so nothing they could do.
Finally, after no longer being able to trust my right hand at all, because it would just randomly let go of whatever I was holding, no matter what size object, I finally went to a DO who takes a wholistic approach. After a few sessions of soft tissue therapy, involving massage, scraping and cupping, combined with stretching and strength training exercises, I'm pretty much back to normal. He worked from my neck down, to get the nerves to "floss" correctly through my system, down to my hand.
I've now moved past the treatment part, but as long as I maintain the daily stretches and strength training, both hands are pretty much back to normal. I do have minimal pain in the right hand if I have a particularly grueling work week, but I'm back to using normal keyboards and even laptop keyboards. And I can mouse and use my phone with my right hand again. I can even trust my right hand to not drop things anymore.
Of course, YMMV, but traditional doctors couldn't get the job done for me. I'm so grateful it didn't discourage me after a years long journey, and I'm grateful for the wholistic approach that worked.