I agree with J649 with absorption. The only thing I would like to add is that B12 (and Folate) can increase histamine and overstimulate some.
Since you said you have blood Sugar issues, have you tried only taking Vitamin B3 in the form Niacinamide (does not create the uncomfortable flush) because that B-Vitamin can actually help with Blood Sugar stabilization.
Aside from that have you ever had a Hair Mineral Analysis to look into your Chromium and Boron levels?
Chromium for Blood Sugar, and Boron for Calcium/Magnesium Usage/Balance which you seem to be having troubles with.
Otherwise with the blood sugar, the only thing that would cause this many problem is if you are real low in Cortisol.
I thought I read you said you had High Cortisol...(this is one of the downsides to Curezone - search for what the person said - is there no way to create a profile for all this to be looked at easily...or am I missing it?)