I have this pain in my knee, my knee almost feels stiff and when I try to sleep at night I become very restless. I used to play volleyball and rugby about 2 years ago. im a very healthy 20 year old female. im thinking it might be bone cancer. my mom had cancer in the past but in her ovaries.
Dear patient Stiffness in knee and pain on single side is Monoartitular arthritis. Most common cause in developing countries is tuberculosis. But it can be also Monoartitular rheumatoid arthritis. Chances of this problem due to cancer is very rare. This needs to be investigated with 1.  X-ray of involved knee anteroposterior and lateral views 2.  MRI of involved knee to confirm diagnosis.  Visit radiology center nearby you and get it done.  Meanwhile, start tab diclofenac 50\u00a0mg twice a day for pain relief and start knee range of motion exercises to reduce stiffness.  You need to consult expert orthopedic surgeon with report.  All the best.