Ugh, so sorry for the rough night!!! I personally have not experienced this, but I do know that B has reacted to some crazy small amounts of things in my milk. And with FPIES, you know the drill-- it is possible. Is there any chance there is anything added to the fish oil or is it potentially contaminated with one of his known triggers? I am sorry-- I wish it was easier. Why can't there be a litmus test for these questions?! Please KUP and I hope your little guy is feeling better very soon!