I agree with Seeker. You are going to want to see a hand specialist for the medical side of things. You may or may not need a referral from your primary doctor in order to see the hand specialist, and sometimes the primary doctor may want to do some initial diagnostics (like x rays). This is all fine, but I do think it is important for you to see a hand specialist.
You have a somewhat complicated history with the hand, and it is certainly possible that x rays would show arthritic changes at the joint that was injured previously. But this does not necessarily mean that the arthritic changes on the x ray are causing your pain (many people have arthritic changes on x rays and do not have any symptoms). A good hand specialist will help sort through which anatomical structure(s) is/are causing the problem, and then determine the most appropriate management strategy. Also, think about other activities outside of the piano that may aggravate/contribute to the pain (we use our hands for so many things!)
If there are specific things that cause you considerable pain, I think it’s prudent to rest from those activities until you are able to get an evaluation.
I think I've mentioned this here on the forum before, but about 20 years ago I had a severe finger injury at work which almost severed my index finger (finger #2 on the left hand if learning piano music) on my left hand. I was working on a commercial A/C unit and got my hand too close to a moving fan blade. The fan blade hit my hand with some force, and when I looked down at my left hand, it was like I had two index fingers; the fan blade had split my finger down the middle from the finger tip to the second joint/knuckle.
It was an awful sight, and the first thought that came to my mind was that my music career was over. Not that I had a music career, but I did play a few stringed instruments, and had for most of my life from a very young age.
I was taken to the hospital and admitted immediately and scheduled for surgery ASAP. The orthopedic surgeon said he had never seen anything quite like it, because the bone was cut straight down the middle of my finger, basically cutting my finger in half, down the middle.
The surgery was successful and the Dr. was able to save my finger, but I had permanent damage to my first joint and my finger-tip. Over time, with some physical therapy, I had some range and motion in my finger, but my first joint was really stiff, and a severely mutilated fingertip.
And, when playing my stringed instruments, the fingertip and movement of the first joint is extremely important. In fact, the injury actually steered me toward learning to play the piano, which I had never really pursued, other than picking out a few chords on the keyboard whenever I was around a piano.
Speaking of arthritis, I remember when I signed the consent form for the Dr. to do the surgery, he mentioned that I could get arthritis in my finger. Fortunately, I don't think I suffer from arthritis in my finger, but I still have the stiff first joint and an abnormal fingertip.
Yet, and still, even with the finger injury, I've learned to play the piano well enough to have a boat-load of fun, and I enjoy it immensely. I wish I had started learning to play the piano years ago, along with my stringed instruments.
Also, I was able to adapt some and I still play my stringed instruments some, but the injury impedes playing the stringed instruments more so than playing the piano. I'm sure I have some permanent impairment in my left index finger when playing the piano, but not a lot, that I notice.
Real Rob, I hope you can get some answers and some relief with your finger joint, and overcome any hindrances the old injury may cause. But do get it checked out as others has mentioned.
Sorry for the long post, but it is difficult for me to make a long story short...
All the best!