Your food allergies come under 'salicylate intolerance' and some foods (very high in salicylates) can cause itching but no rash. Vomiting to codeine is an intolerance and unrelated to the food allergies.
You could have urticaria and just like diabetes (autoimmune condition), you should get a complete blood count
, TSH profile done with TPO antibodies
to exclude a thyroid disorder
It quite often co-exists and a TSH alone is not sufficient to find this autoimmune hypothyroidism
Long acting antihistamines and thyroid treatment (depending on results) could lead to much better control of symptoms.