Google throws up something called tendinopathy which can be caused by driving, which was presumably considered by your healthcare providers?
Anyway, plenty info via Google about that kind of thing, which presumably you've already looked up...
But certainly wouldn't be surprising - I suspect all of us have some kind of aches and pains caused by driving, especially as most of us are getting on a bit, and doing a lot more driving (or just sitting in relatively cramped position) than the average
Of course, the most obvious solution to your gear-changing problem shouldn't need pointing out here. But, equally, it's not the kind of thing that's simply like changing your seat position, or whatever
But my occasional back pain is one reason I got an automatic when I changed my car last year - not that I would have got rid of my manual car because of that, but because I had to change the car anyway it seemed a good time to dump any possible future pain caused by pushing that clutch down
Another minor issue is occasional discomfort in the area where my leg meets the groin (8-[ ) which I think is a tendon or whatever, and which came on in 2006 when I got a new car, and think the seat was sitting too far forward, and this caused it, and it's never been the same since, although I don't think changing gear has ever helped it, although other stuff like my exercise bike can bring it on.
Not that that has anything to do with your problem, but just to illustrate the importance of stuff like seat positioning and the like, particularly for us high mileage drivers.
And another thing to watch in particular is that if you've been doing something like driving a particular car or maybe riding a particular bike for a long time, changing to a different one can cause issues until your body adjusts or whatever.
But, of course, plenty stuff available online about more general issues like that, so no point my blabbering on about them here...