I've just come to the realization that what I thought was joint pain from arthritis may actually be tendinitis. Nothing in particular seems to bring it on (e.g., overuse). The pain starts off gently in a very specific location near a joint (I can use my fingertip to isolate it), but increases with time and ends up affecting the nearby joint in terms of pain and mobility. After a couple of days, it's completely gone but then reappears somewhere else. Is this a sign of tendinitis?