My Left Buttock And Thigh Has Had Me Down For

My left buttock and thigh has had me down for four days it doesn't go down my leg start at back then but and knee. just left side hot shower and aspcreame doesn't help. Had knee surgery 4 years ago same side. What do I need a shot what is this? Thank you so very much. Also what sure I expect when I have my lumpdetogy I know spelled it wrong?