With children the allergy or as you more correctly say sensitivity ,may have several determinants
1. Was the chilld born normal or cesearian?
2. Breast fed, if yes how long?
3. Did you have a healthy pregnancy?
4. Do you share any of the sensitivities?

How old is your son?
Is he otherwise well, happy and content?

Did he have any infant infecxtious episodes? Especially ear problems or skin.
Has he ever had antibiotics or did you whilst pregnant?
Have you tried probiotics and food restriction ?
Are his stool ochre in colour, homogenous and floating?
Does he have a coated tongue?
Is he in any pain?

Then I may be able to assist if that is what you need.