J.S.
Your son is having gastronintestional problems, the behavior follows the pain. I bet you sense that? I would highly recommend you get him tested for food allergies and food sensitivities (IGG test). Don't let the ped tell you it is behavioral - sorry, I massively disagree. Especially when children change behavior (usaually not for the better) when they have to go indicates pain in the gastro track.
If you want some real experts, you should do a phone consult with The thoughful House. They are doctors who specialize in Autism. Don't let that scare you, because Autistic children have the exact severe gastro problems which are usually ignored, but this group is awesome.
Dr. J. Buckly, MD is a pediatrian in Cumming GA (also with a practice in Jasksonville, FLA) also with a specialty in this area. Most doctors just dont get it, even most specialty gastrointionoligist do not provide these kids with solutions. These doctors do. There are other DAN! docs around, all who understand this issue. www.generationrescue.com has a list under providers, I think.
Dont wait, your son needs you to look at his health, not at his behavior. He is showing you a problem he has no idea how to handle. Pain in the gastrointetestional is aweful and knawing.
I would immediatly take your son off milk products, and work your way of gluten. I garentee results. Check out gfcfkids.com for a good diet plan. You are going crazy, what do you have to lose?
J