Natalie, I believe there are some people on this forum with B12 deficiencies, so maybe they can respond about the B12. I was diagnosed with Graves Disease, but then my thyroid went from overactive to underactive and my diagnosis was changed to Hashimoto's Thyroiditis. It is an autoimmune disease but I don't think it shares many symptoms with Crohn's, so I'm not sure what symptoms brought you to this site. Hopefully someone else can help you with the B12 question.
Crohn's Disease, Acid Reflux/Gastritis, Hashimoto's Thyroiditis, Endometriosis, Arthritis, Depression/Anxiety. Too many meds to list them all. =)