What Does A Painful Rash On The Lower Back Indicate?

Hello, I am wondering about a large and growing skin rash on my lower back, and spreading around the side to the hip and upper leg. It does not itch, but is generally sore. The soreness disappears when I take aspirin. I have some small hives on my arms that are a little itchy, but that is not unusual for me. I am wondering if I need to set up a doctor s appointment, or if I should wait and let this run its course. I have used hydrocortizone ointment on the rash, but it has not reduced it or prevented it from spreading. LP