Tell your teacher. Perhaps there is a way to change your technique to relieve stress on a particular muscle or tendon. A doctor who is familiar with instrumental technique can analyse what is causing the problem and suggest solutions. Some doctors specialise in keyboard instruments, wind instruments, string instruments, etc. Try to stay in good general physical condition.
Normal exercise can do a lot to prevent over-use.
This information, based on personal research and experience, is not professional medical advice. If you want professional advice, seek a good physician. These simple remedies were suggested by her physical therapist. Also stretch your arms with palms together, fingers pointing up, then down. I'm sure that there are many other stretches.