I would first start recording when you see reactions after eating which foods as it could be lots of things. Allergic reaction on diary, gluten, nuts, eggs, fish but more and more we see allergic reactions on additives and preservatives too.
I’ve a wee book called the “Additive Alert” which I found an eye opener and very helpful.

It could just be their little tummy adjusting to new foods. If it gets scarey, I would suggest you go and have him checked out. For your peace of mind if nothing else

Please get an allergy test done.

I would imagine he would be sensitive to certain ingredients in the foods. You can visit the GP to arrange an allergy test, and then you will know 100% what the issue is

Hospitals can do allergy tests.

Could even be a preservative allergy. When I was a child I and allergies to certain preservative and flavour enhancers.

Lots of people have mild reactions to different additives or plants but without tests you won’t know which particular ones your son is reacting to.

He might be sensitive to a certain ingredient . You might need to do an elimination test one by one to find out what it is. Ask your family GP or nurse at the Childhood clinic.

Check with a Dr for allergy testing. It could be particular additives not just the main ingredient.

I think you sould ask a medical professional.

He could have some allergies or intolerance to certain foods. Better to talk to your GP that maybe will send him for allergy tests.