How Should Knee Pain And Stiffness Due To Trauma Be Treated?

I banged my knee about 3 weeks ago against a chair. It hurt when it happened but I was able to walk and do everything else fine. Im a runner so I continued to run and workout thinking it was no big deal. eventually my knee started to hurt while running to I eased up on the running. After I would step off the treadmill my knee would be fine. Eventually my knee started to hurt just by walking. I started to apply RICE. the pain has decreased however I still feel stiffness when I stand, some pain when I walk up and down stairs, and occasionally pain when I'm sitting or laying down. I so badly want to go back to the gym and continue working out my upper and lower body but I'm afraid it will affect it more.