Thanks for your query.
Looking into you matter as per you said only the knees are having pain , no other involvement of small joints can be made out . You havent mentioned your age and weight , otherwise that could aid in diagnosis because certain arthritis occur in particular age groups. Anyways I advise you to consult a rheumatologist
and get few blood tests like ESR
, CRP , RF, S. Calcium and Xray both knee joints , to assess for any evidence of arthritis.Osteoarthritis
can be one possibilty in your case. Your problem needs detailed evaluation at earliest . Kindly dont delay and visit your doctor early.
Wish you a good health