another possibility would be low blood sugar. Are you, by chance, hypoglycemic? If you are, then it's especially important to eat regularly and not go more than 4 hours without eating at least something. It's also important to keep your choices low glycemic to avoid spiking and crashing your blood sugar.
With so little to lose, I don't honestly believe that you need to be going as low as 20 grams of carb per day. Perhaps starting somewhere in the range of 45-60 would fit you better and you can go lower gradually if the weight isn't coming off.