It sounds like you may have candida -- an overgrowth of yeast in your system that can create digestive illness and foggy thinking/lack of concentration. Many of us with bulimia have it, although most doctors don't know how to test for it. Consider picking up The Body Ecology Diet, by Donna Gates. It is a way of eating that creates body repair and starves off the yeast. It takes commitment and dedication -- it's not a quick fix. But it works. If you've tried everything else and found nothing that helps, try this. After 16 years of bulimia & trying everything under the sun -- this did it for me. I am now recovered, no more cravings and I feel great.
I write about it in my blog, if you want more information. http://TranscendBulimia.com -- it's down for maintenance today (3/12/06), but will be back up shortly.