magnesium has been implicated in insulin resistance, something doctors rarely test for along with glucose. the fasting insulin level test seems to be somewhat helpful.
insulin resistance causes the body to ask for more insulin than needed in response to carbs, which causes resultant fatigue, storage of the carbs into fat, and the cravings rebounding back.
magnesium deficiency in lyme has been discussed in other threads.
here are some articles linking magnesium depletion to insulin problems: