i experienced something similar with my baby girl and the only thing that worked was this over the counter stuff called domeboro. it came in little packets that you just mix with water and soak their tush in. it was the only thing that would work and it helped immediately! i think you may be able to find it at walgreens.
we have seen a dr for my baby's very severe diaper rash and are using rx cream but nothing seems to work. she has had the rash for about 2 weeks in different states throughout. it has been the "1 step forward 2 steps" back sort of thing. she has open sores that have gotten to a point where they have shrunk but refuse to heal any more. she has also been on oral antibiotics for 3 days now. today the actual 'rash' part of it that we thought had finally gone away has resurfaced with a vengence. . please help with any suggestions.