How Can pain In The Elbow And Knee Be Treated?

Hi Doctor, I was running in full speed on the road inside our academic campus and fell. As a result my knees and elbow got hurt. Of all the wounds, one wound on my knee is a little big and slightly deep. I cleaned it with normal water and then with liquid dettol. It seemed okay, until one morning when I observed a cotton thread from blanket gotten stuck there, when I removed it, it started bleeding (very little). I again cleaned it with liquid dettol. I sometimes put petroleum jelly on it. Now pus has formed there. Today is the 5th day of my injury. What should I do? Please guide me. P.S. I did not take a tetanus vaccine this time. The last I took was on March 20, 2016.