<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, I have been having a lot of arm pain lately and my knee hurts too. Also, I noticed some swelling in my elbow. What could be the cause of this?  <response>: It sounds like you may be experiencing bursitis. It is an inflammation of the bursae, which are small fluid-filled sacs that surround the joints and cushion the bones, tendons, and muscles. 