janindaboo,
Hi, I'm a serious piano student, 21 years old, preparing for a performance career. I was injured while doing a solo concert series last fall, and I've been dealing with the repercussions of that for just over a year.
First thing you need to do is see a hand specialist to rule out any bone spurs, congenital defects, etc. I doubt it's any of those things though personally, all the same, rule it out. I did that, and was diagnosed with Tendinitis, did the physical therapy thing for several months to no real effect, went back, got an MRI, and then the doc overturned his diagnosis and said he simply didn't know what it was.
The solution for me has been retraining, which I've been doing for a few months now. I was playing and performing everything, Kreisleriana, Beethoven's Appasionata, beginning work on Rach's 3rd, etc etc. The problem that lead to my injury turned out to be a physically damaging technique. Things like dropping the wrist on chords/octaves/etc, stretching (even visually small stretches can be damaging, if you do them enough - there are other ways)
What you will find eventually, is that even if this problem goes away safely and you forget about it, it is very likely to come back later in life if you don't address it. I know how impossible it seems to cancel concerts and festivals (I had to do that myself... very annoying) but your body is telling you to do something differently, via the medium of pain. PT/OT will alleviate symptoms most likely, as will time and cortisone if you go that way, but it still won't address the root cause.
Look up these people
https://www.golandskyinstitute.org/., and the associated method. This is what they do. DO NOT start reading guides and forum posts on the internet and start trying to retrain yourself - it won't work, you need someone to watch and coach you, no matter how much you know. Even Olympians get injured, and they go see people who help them move past their troubles.
They're controversial in the piano community, and people are bound to get on my case for posting this but believe me. I've tried everything short of surgery, and this is the only thing that is helping me move forward. Give it a chance, it's probably your best bet. These people know what they're doing. Go to the summer symposium and find a qualified teacher of this method on the website.
I don't want to bore you with a long post, but if you have any other questions just PM me and I'd be happy to talk about injuries and solutions.
It makes me very sad to see people injured, I've been through and am continuing to find my way out of the hell that is a performance injury. I hope you get better! best of luck.