hummm... how about B12/pernicious anemia?? If your having an absorption issue secondary to your rapid bowel transit, causing malabsorption of vitamins, including B12.. what is your MCV on your CBC profile?

I know when My GI issues are bad, that I don't even absorb my oral meds .. its awful.. and sooo frustrating!

They put me on plaquenil for the joint pains and muscle fatigue - it helps a lot.. though it does have some GI side effects initially....
Good luck!! keep us updated!