My grand daughter, 18 months old, has developed a rash on her lower back that is getting progressively worse. Welt-like and seems to itch as she keeps reaching and pulling at her diaper trying to scratch it (it's not on her bottom, just her lower back) It's spreading quickly. No changes in detergents, soaps, cleaners, no recent vaccines. Only change is I bought her some new clothes and I told my daughter it may be the dye in the clothing since she didn't wash them before letting her wear them. I instructed her to put an anti-itch cream on it and give her a half dose of childrens benadryl and to call me back in 30 minutes. They let her play in the tall grass along side the river the other evening while they were fishing but it doesn't appear to be "bug" bites...any ideas???