Sarah, the first thing to do is to get past the idea that just because something is natural it will help excema. That is no more a quarantee than it coming from a pharmacy would be. Problem substances can come from either souce, as can helpful ones.
What is needed is to get rid of whatever the allergen is that is causing the reaction. Yes it does take a couple of weeks for the stuff to clear your system, and then a bit more than that for it to clear the child's. Whether that allergen is food or some other environmental substance, it takes time and paying close attention to figure out what it (they) may be. If you don't see results with the dietary changes, I suggest you 1)stick with them (Rule one in science like this is to only change one thing at a time so that you Know what made the difference); 2)try different detergents, different soaps to see if they are the source of the problem. Read labels, compare ingredients.
I forget which ingredients are supposed to be the worst offenders in stuff like lotions, but I do recall polyquarternium or quarternium15 or whatever number, or something like that, supposedly being a problem for many. Lanolin is a big problem for me, which is frustrating when one of the most recommended soaps for people with excema contains it.
The best thing to do IMO is to stick with single ingredient items for baby's skin: olive oil or coconut oil to keep it from drying out. Tepid baths, only 3-4 per week at most, pat skin dry rather than rubbing, apply oil lightly. One of the things with adult excema is to stop the constant wet-dry cycle which is what helps aggrevate the problem. Same for baby from what our first ped advised us when DS was having a bit of an issue.
FWIW, what we use here is: Lubriderm for Seriously Sensitive Skin for lotion, coconut oil for after shower (when the Neutrogena runs out
), Granny's Power Plus Laundry Detergent for clothes washing. Some might say that the Granny's is not "natural", but by golly it's got nothing in it but water and nonionic surfactants. No brighteners, colors, masking perfumes, florals or any other nonsense that pretty up the ad copy and may or may not do any actual cleaning. Thus it also has nothing to cause skin reactions.