Have you ever tried Beano? It's a digestive enzyme that can help you digest beans. Since soy is a bean, it can be very helpful to take before you drink that glass of soy milk. Also, I don't know about the reaction you had, but I do know that gas is a normal side effect of any soy product if you're not used to digesting beans. So the good news is it should go away. As for it acting as a laxative, I'm not sure! Maybe someone else has a better answer to that one.
-------------------- "Anyone can exercise, but this kind of lethargy takes real discipline." -Garfield