You could be hypoglycemic, even if a test wouldn't show it. My experience with "sweets" and "starches" is that they are unfortunately just as bad for me as eating a cup of straight table sugar. Doctors have always said my blood sugar levels are normal, but I crash less than 30 minutes after eating anything sweeter than a piece of fruit. And when I say crash, I mean either I eat more sugar, or I pass out.
Try eating no starches (no fruit juice or white foods - potatoes, pasta, bread, dairy, sugar) for a full week, and see if that helps. Have a piece of fruit with a handful of unsalted nuts between each meal. And make sure you never go more than 3 hours without eating something.
Also, be sure this isn't related to caffeine by not having any for at least a full week. Caffeine addiction is just like sugar addiction: A few days without it will give you headaches and make you feel awful, but by day 7, you should feel normal again.
I take a B-12 supplement made by Solaray that is vegan and made in a base of whole rice and aloe vera gel. I take this every other day and feel that my energy level is much improved. Alicia even recommends it in her book.