to be honest i would expect a food intolerance/allergy to cause a more widespread rash then just the back of your hands.
sounds like yo need a few weeks of strong topical steroids and emmollients to calm it all down
Immunology is viareferral from gp but waits are long as allergy specialists are few and far between on the nhs. I think there is only one immunologist for the whole of the southern half of wales for example!