Allergies

I had rush my 6 month old to the hospital today :-(
I think he had a reaction to the change of formula, as his mixed fed with nan ha gold. Silly me brought nan pro gold because our store didn't have the ha!
After a few mouthfuls of the pro he started vomiting, got a massive rash & started to get really tired & floppy :'( I never want to experience that again!
I did some research on the difference between the formulas.
NAN HA gold has 100% whey protein.
NAN PRO gold has 70% whey protein & 30% casein protein.
My question is was your child allergic to the cesein protein?
Did they grow out of it?

( I mix feed with formula, as I'm weaning him off the boob)