Hi Laura,
You might find this website about chronic fatigue syndrome helpful; the bloggers most recent post describes how weekly vitamin B12 injections have helped him. The more I think about it, the more I feel that your issues are caused by severe nutritional (vitamin?) deficits caused by malabsorption from your gut issues.
http://www.chronicfatiguesynd.com/
I find it so disheartening when I hear stories like yours where doctors just give up, or even disacknowledge, when they can't find the problems. Bad medicine, I think.
I think the Cleveland Clinic is a great idea, and I truly hope they will uncover something and be able to fix you.
Take care,
Nicole