I agree, not a dairy issue. My son has a milk protein allergy and he reacts when I eat anything dairy and it comes through in my milk. Sounds like you have a good plan to see if one of the food items is disagreeing with him.

Don't feel guilty for most babies won't react badly to the prepared food. I"m the only person IRL that I know with an allergy baby and having to introduce one food slowly at a time to test for a reaction. Everyone else is feeding their bub this and that without worrying too much.

Hopefully the problem will be sorted soon and I hope the reaction doesn't last too long.