skin rash

munchkin1025

My LO has a rash in the folds of his legs behind his knees.  No bumps or anything; the skin is just red.  We have been very careful about keeping the area dry.  We tried hydrocortisone - the pediatrician's recommendation.  It hasn't improved much at all.  We were thinking that maybe it's a fungal infection and plan on calling the office again tomorrow.  Anybody have a similar type of rash?  TIA.