A.,
My little one has the same issue except his is in another category I guess because it's so severe. With him, the dermatoligist that he saw suggested over-the-counter treatments included using Selsun Blue and just bathing him in it. Also at EVERY diaper change, rub him down with Aveno, dry/sensitive skin lotion and alternate with a product called aquafore......it's kinda like vaseline. These products work very well for my son when he just has the mild cases, but when it gets really bad, he has a steroid that I have to put on it called Cutivate and prescription strength hydrocortizone.
As far as being allergic to his soy formula, it's possible. Or it could be an allergy to the laundry detergent, something in the carpet or even something in the air. We found out that our son is allergic to all dairy, eggs and peanuts, but that he's also allergic to animal saliva, because he can play with the dogs and cat all day and never really have an allergic reaction, but one of them can lick him and he turns into a little red lollipop. We also think that he could also be allergic to something outside that comes in with him after his brother and sister have been outside playing or if the animals come in from outside.
I have come to learn that eczema and allergies come hand in hand, because everyone that I know that has a child with eczema or atopic dermatitis, also has a child with moderate to severe allergies.......
Hopefully your son is the exception to the rule. Good luck, hope my experience is able to help you out.