Have you looked into diet???
My DD was diagnosed with Excema & had the same problem with creams not working, but thanks to info from a friend who works in Childrens alternative medicine, realised it wasn't excema at all, but urticaria caused by intolerance to food colourants & preservatives...google Azo Dyes & Benzoate preservatives, as they tend to be the biggest culprits, though DD also has problems with MSG, & sweetners too......... they pop up in all sorts, even though we knew DDs problem & therefore her nursery did, she once ended up with a bad ongoing flare up, because they were giving her bagels as at snack time, they thought they were fresh baked, but contained the preservative as they go off quicker due to extra sugar.
if you are still breast feeding, as I was at the time, it can be what YOU are eating, & its passing through your milk to DD,
If you've already lookied into that possibility, then there is a herbal cream, Zambesia Botanicus (I think) , or Sausage Tree cream, (herbalist or good health food shop) its brilliant stuff for Skin problems, & it works well on true Excema too, I've an American friend whose DD has true Excema & she always stocks up on it for her DD when she visits, as it works better than anything else for her DDs ....its not cheap, but spreads thinly, so lasts a long time, so does work out cheap.
Also, my DD used to get bad flare ups in her groin & top of legs, & like your would howl when she wee'd........ I used Metanium cream as a barier on advice of our chemist...also brilliant stuff
good luck, I feel for you, I remember how awful it was...thankfully DD now has beautiful skin, never has a problem, bar the odd minor flare up if she eats anything with artificial colours at parties etc