@fBoyle-- There are some very effective over-the-counter topical creams for diaper rash you can try. Just ask a pharmacist about it.
This might sound weird but there is a type of cream that's also sold at pharmacies now. It's originally a cow udder cream but it's a multi-purpose product and good for lots of things including dermatitis treatment. It relives rashes and itching, moisturizes and soothes.
Another good remedy is good old lard. Lard along with corn starch is what our grandparents used to use for diaper rashes. Lard is soothing and moisturizing and corn starch absorbs excess moisture and prevents more rashes from developing.