I got tendinitis in my middle finger from doing too many kettle bell swings, tendons don't give a warning, one day zero pain, next day so stiff I couldn't bend it. 90 days in a splint made out of coolant hose and duck tape till I could bend it again. tendons take fucking forever to heal. if you didn't actually injure it, it's just inflammation, the only cure for that is immobilize it and massage it, then lots of time