Suggest Treatment For Knee Pain

Knee Pain. Ive had a pain building up over a period ot time to which after playing volleyball last sunday I had much trouble putting pressure onto the knee by bending ( going up the stairs etc ). The pain did go away and I went training last night to which I am now even worse with the pain. I have heard some horror stories to tendons and knee ligaments and dont want to put myself in a scenario were I do some major damage. Any ideas what this might be and how to get a good diagnosis on this quickly.