Becuase this is a board where people ask questions and other people provide their thoughts?! It's up to the OP how he much he takes on of what people write.
True poncho, but common sense goes out the window with some of the answers, my TB infected my lungs, knee and spine so I could have said "blooming heck you may have TB in the knee". For all we know the OP could be the gullible or sensitive type who takes it all on board reads some replies and throws an anxiety attack.
Look for the simple and obvious answers, see if the pain and swelling goes, if not go to your GP.