Hi there.
This is good advice, for a start, to relax. However, I know this is easier said than done.
I a writing on thsi post as a family friend who was a concert pianist, now passed on, experienced terrible pain in his hands and arms, in his late thirtis, and nearly had to give up the piano. This situation forced him to learn the anatomy of the hand and arms. and develop his own technique to resolve these problems. He also had small hands, which did not help initially, but he developed a technique of strengthening his fingers, and in fact, being able to return to the piano, and play very much better than he did before.