Extreme sensitivity on lower right knee cap

[Acinom7777]

This has been reoccurring for 3 years or so.  I can run, jump, etc....but I cannot kneel even on a soft surface.  Today I had capris, and he slight friction from the pants to my knee cap as I got in my car was sudden and excruciating. It feels like a tendinitis or something?  No noticeable swelling, but feels tender and somewhat soft in the area.  The sensitivity comes in waves, maybe every 3 mins or so, goes away, then surfaces for no particular reason I can mention.  Any ideas???