I have no idea what's causing it...all I know is that I am a hard-core sugar addict, and I need to stay away or it gets out of control...I eat lots of natural sugars, but as soon as I have one taste of the other stuff I go nuts. I read this book:

Lick The Sugar Habit

and it had a lot of scientific sorts of ramblings about how eating dessert can mess up all the other digestion of the other foods you ate for a meal...in a chemical miscombination way...I recommend reading that, if you're serious about giving up white refined sugar. It's sort of convincing and sort of you have to take it with a grain of salt. I used Nature's Plus "Ultra Sugar Control" to wean off sugar...it's L-Glutamine, which tricks your body into thinking you've had your sugar fix. I found it on-line. It's supposedly good for alcoholics too. But yeah, my yoga book says, "sugar destroys the life-force." I believe that. But our culture and holidays revolve around this very addictive substance. Try deleting it from your diet for a few months...see how you feel. I'm sure you'll notice a huge difference.