Suggest Treatment For Pain And Swelling On Knees After An Injury

I fell on my knees on blacktop six days ago. Xrays at ER negative. LARGE swelling My own physician follow-up yesterday. He said okay to walk. Today leg becomes very, very painful at four hour dose of aspirin as it gets to the end of four hours between aspirin. Why so little--if any-- improvement after so long in regard to pain and swelling and throbbing.