Food protein induced enterocolitis (FPIES) - Any experience?

Hi,

My DS2 has fpies :(. I thought I'd check here if there was anyone with experience. I did a quick search but just found one very old thread.
So far we know he reacts to cow's milk, soy, eggs, sweet potato, and possibly fish. Severe vomiting exactly 2 hours after eating, pretty well passes out between vomiting episodes, finishes up vomiting bile. Followed by a couple of days of diarrhea.
The main difficulty I'm having at the moment is that he seems to be fine the first few times he has a food. So we introduced all sorts of things and thought he was fine with all of it. Now he's developing reactions the 5th or 6th time he has something so lots of things which I thought were safe are turning out not to be.

Kind of hoping no one else's little ones have gone through this, but also hoping for someone with experience :)