My now 11 month old has had terrible excema, here are some things that have worked for us:
I spoke to several doctors and a homeopath, none of them recommended taking anything out of my diet while breastfeeding. They said the length of time it would take to possibly get any conclusive result would not be worth it in comparison to the nutrient we were both getting from my diet. If it was a severe food allergy, there would probably be blood in the diaper.
Mitten cuff sleeves all the time, day and night.
100% cotton clothing, turned inside out if the seams seem irritating.
All-natural, residue free, enzyme free detergent (I use Mountain Green Baby) or olive oil soap grated and dissolved in water and used as laundry soap.
Cetaphil Cleanser instead of soap. No soap.
Cetaphil, Eurcerin, and Aquaphor - several times a day, thick layers.
Either long stretches with no bathing or long luke-warm baths every day. Oatmeal baths, Aveeno makes one.
Hydroxazine (rx) for itching relief, get it from your pediatrician.
Minimal use of steriods, like cortisone.
It's very difficult to deal with.