If you haven't corrected the diagnosed B12 deficiency, get that taken care of.
Sometimes cod liver oil capsules, depending on brand, aren't actually very high in vitamin D. I like the "Blue Ice Gold Therapeutics" CLO from Green Pastures (I take it and carry it in my office). I do think it could be helpful.
I do phone consultations if you are interested.
If you want to test yourself for gluten sensitivity, I highly suggest www.enterolab.com
, while you're getting that you might as well get the other allergens they test for thrown in--dairy, eggs, soy, yeast.
I do believe that Robb's suggestion of insulin sensitivity potentially being a huge factor is likely correct as well.
Dietarily, this will mean:
Low carb diet (no artificial sweeteners!)
No nightshades (that's my own addition to the list)