Are you warming up your body prior to play. I am not talking static stretching for your warmup. You can perform some static stretches at home -- 30-60 minutes before you plan to start hitting. Once you get to the court, your warmup should be dynamic -- it can/should include some dynamic stretching.
Have you been using a racket that is too light or too heavy for you? Perhaps the grip size is too small or too large for our hand. You may be squeezing the handle too tightly. Are you using stiff strings, such as polyester? 1-handed or 2-handed BH? You might consider switching to a more arm-friendly racket. What are you currently using?