The manufacturer states that the vitamin E is from soy? Generally it is from wheat/gluten, unless the product is labeled gluten-free.
I don't really know much about soy as it seems to be tolerable in our little girl, but I am with pp in the idea that you should probably remove it completely until he clears up and then you might see about adding it back to test for a reaction.
Most of the time I call about vitamin E, I'm told that it is derived from soybeans and carried in soybean oil. Sometimes I'm told that it's derived from/carried in wheat germ oil. Rarely, I get told sunflower or sunflower, and occasionally I'm told that it's synthetic.
I do react to vitamin E derived from soy. Most folks allergic to soy will not react, but some of us do.
Chasing DS since April 2007 and pumping for DD March 2013.