I was thinking metabolism, too. My doc says hot peppers increase metabolism. I don't like them, but maybe you do. My metabolic rate, measured at a wellness center, is abysmal; I can only eat 800 calories a day without gaining. Maybe yours is really low, too.

My doc is also going to put me on metformin, but that might be too extreme for some docs to want to prescribe. I encourage you to Google ways to increase metabolism and try them. As I know, it's a miserable feeling to work your gluts off and and not lose any weight or even gain.