I have an 11 year old girl who has a dairy allergy. Have you tried to eliminate ALL dairy... even the hidden dairy? Beleive me dairy his hidden in EVERYTHING. (like chicken flavoring in different food items... Ramen, etc... who knew)
My daughter breaks out in the worst hives/eczema!!! It is horrible... painful, burning, etc. We discovered her allergy when we switched her from Soy formual to cows milk and it is to this day a learning process.
Another food ingredient that can create similar reaction is GLUTEN. Again, a hidden ingredient in many foods.
I went with an elimination diet. Started with all rice diet(very few people have rice allergies/intolernece) and then when she was better added one food back into her diet at a time. Get used to reading labels, labels, labels. Do research on the internet to acquaint yourself with other names for wheat/glute/dairy etc. (in hte case of dairy, whey, milk portiens etc.)
Hope this helps! Good Luck