doesn't sound like it's a detergent problem but I used to just was the kids stuff in 2tbs of bicarb. Works just fine.
Poor little guy. HOpe you find a solution - from personal experience I know how frustrating it is. I know mine gets worse when I have too many tree nuts or too much unrefined suger.
I just want to know if there's a trigger or not and then I can deal with it either way.... so looking forward to the specialist appointment in that way - if there's no trigger I can deal with that, if there is a trigger, I can eliminate (as much as possible) that as well.