That's a tough question to answer. Since you tolerate soybeans you may not be allergic to soy protein. Most people allergic to soy protein can tolerate some soy products. Soy sauce is made by fermenting soy beans and this appears to render the allergens inactive for most soy-allergic individuals. Soy lecithin is a fat and contains no soy allergen (unless as a contaminant) so that too is typically tolerated by soy-allergic persons. Soy "milk" is not a true milk and often contains other ingredients to make the beverage more milk-like in consistency, smoothness, pour-ability and taste. Some of these ingredients may be vegetable gums or natural flavors. You might be allergic to these extra ingredients rather than to soy. You should be able to resolve this problem with the assistance of a board-certified allergist. Alternatively you could try other brands of soy milk to see if this problem occurs with all or most of them or with just one brand.
Steve Machtinger, MD FAAAAI