Hi Jill, big hugs to you! It is so hard to see LO suffering. Also for Vicki!
I have been suffering very complicated allergies but I am pretty healthy now and no need to avoid any food at all. I went for alternative allergy elimination treatment which work very very well for me. If you are interested, I can give you more info but I understand many people are skeptical and I respect that.
One thing you can do is to keep a journal of food and drinks he has and also the reaction, in your case is BM. I started keeping my food journal since May and from that I could see very clear patterns of what might be the trouble makers. By going through it over time, you will be able to spot something. You can then go on elimination diet to try. Some people might tell u to go off dairy, citrus, wheat or what not, from my experience with allergies, all kinds of foods/drinks can cause the same reactions, so what one experiences can be totally random compared to the next.
My journal is very simple, I just put down BF, S, L, S, D (breakfast, snack, lunch, snack, dinner) and add reaction, say constant BM, soft, stinging, rash, etc at when it happened.
It is a long journey and more hugs!