I don't know that piece, so I can't say anything about it. What is it in that part that gives you problems? Is it octave runs, repeated chords, ...?
Also, your description of the pain is still not detailed enough. Where exactly is the pain (e.g., 2 inches from the base of the thumb, underside of ther arm)? What type of pain is it (sharp, very localized, broad, burning feeling)? Does it go away when you stop playing or does it stay for days?
X-rays will probably tell little, but going to a doctor might be a good idea. But first, what does your teacher say?