Did you ever find out what was happening? I, obviously, hope it was something like different wipes, but did you get any clear answers so you could stop worrying?
My DD had a butt rash for over a year that would just not go away. At the time she got it, we had been at the beach and she was in swim diapers all day. I never made the connection that it was Staph until I got an infection during my breast reduction surgery this April. My doc had me swab her to see if she was the source of my staph. Sure enough she was. Poor thing has had it for a year!!!
She went on antibiotics and it cleared up but is coming back so we might have to take other measures. I am kind of worried.