Baby rash - any idea what it might be?

My 9 week old has a bumpy rash on his tummy/arms/legs but not on his face/head/hands/feet/back.  It's flesh colored or just slightly pink, I can barely see it on his legs but I can feel it.  He isn't running a fever and is acting happy and normal.  I had a pediatrician appointment last Friday and he said it didn't seem like anything to worry about and that it might be irritation from clothes rubbing or to some soap/lotion. I think it got worse today and I'm wondering if I should take him back in or not.