How Should Knee Pain On Weight Bearing Be Treated?

I've got a terrible pain "inside" my knee (it feels 2 inches deep, i guess) it hurts to bear weight, to bend, even to keep still while i try to move the rest of my body. The pain has followed a day full of kneeling, squatting and standing, and brings tears to my eyes. How long should I wait it out before going to the doctor?