D.H.
I think he could be allergic to the soy, but ALSO have trouble digesting the soy.
When my son was born the hospital had free samples of a soy-based formula available. I didn't feed it to him then, but when I (reluctantly) gave him his first bottle, it was that stuff, because it was all I had & I didn't know what to give him anyway.
He was fine on it for quite a while, but then started getting all gassy & uncomfortable. His doctor then recommended GoodStart. Then things got better.
So it may just be a thing with soy. I have problems with soy-based things, too. It must be the type of protein in it.