<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, I have been feeling extremely tired lately and my knees are always stiff and tight. Also, there is a lump on my knee. Can you tell me whats wrong with me?  <response>: Based on your symptoms, it is possible that you have a cytomegalovirus infection. This virus can cause fatigue and joint stiffness or tightness. The lump may also be a result of the infection. We will need to run some tests to confirm the diagnosis. 