Why Is My Knee Hurting While Taking Right Or Left Turn?

I hurt my right knee by trying to cut someone (sudden push off my right leg to change direction from right to left). I could not walk down the stairs without it hurting or me holding onto the railing for about 2-3 days. Its been a week now, and although it has been getting better, I still cant run properly and Iam very nervous of putting pressure on my knee. The back of my knee hurts when i extend my leg fully, but the pain in that area is decreasing per day. Im assuming its a hamstring tendon at the back of my knee but Im not sure. Is there any possible answers to what has happened to my knee? Is it normal not being able to run a week after the injury?