hello. Welcome to HCM.
Pain in knees on prolonged sitting and inability to unfold without pain signifies beginning of arthritis
. You have to gear up for regular exercises, which might not benefit you immediately, but will help a lot in avoiding problems in old age. There are definite exercises for knee pain
of this king. A good physiotherapist will demonstrate you. Please spend at elast half an hour in morning with them. also make sure to avoid sitting cross legged or any activity which requires complete leg folding at knee.