Your story is so physiologically improbable that it makes me wonder if you have some variant of Kleine-Levin Syndrome (sleep disorder with compulsive hunger/eating -
Kleine-Levin Syndrome Foundation Inc. | What is Kleine-Levin Syndrome?), which because you keep such tight psychological and behavioural control of the hunger during the day, has resulted in Night Eating Syndrome (a sleep eating disorder -
Night Eating). Maybe you gain weight on more than 1500 calories/day, despite exercising, because you're eating tons of calories in your sleep.
From the sounds of your responses, you feel like you've tried everything, when in fact, it sounds like there's a lot you don't know. Your medical, nutritional and exercise knowledge base in this area is not comprehensive enough to conclude that things are hopeless for you. Yet, you are reluctant to seek expert medical advice. I don't know why you're aversive to seeing doctors, but as an MD myself, I do hear this a lot from patients, and I think it's important to get past for health reasons.
In the end, I think a big problem for you will be that your problem is multi-factorial, so you will need the opinion of a number of medical experts (maybe a geneticist, an endocrinologist, a psychiatrist, a neurologist, a sleep medicine specialist, etc.) to get a final diagnosis. In the Canadian health care system where I am, that may be more feasible to do, so maybe I'm biased by not knowing your situation. At any rate, your family doctor should be the place to start.
Good luck.