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. Additional information and corrections, if any, are always welcome. This can, for many people, be a useful preventive and curative method. A search on the web should reveal plenty of further information.