Wow, you have my sympathy.
It doesn’t completely support what Nathan said, but formerly fat people have a much harder time staying at a normal weight than normal weight people. Not only do their metabolisms plummet, but they are literally driven insane by their bodies. http://www.iht.com/articles/2007/05/08/healthscience/snfat.php?page=1
Unfortunately, the only way nonsurgical, reliable way to get thin is to not to get fat.
Sorry if that was depressing, but at least you know you’re not a freak...
Normally you'd eat say, a ham sandwich 30g carbs, a bowl of vegetable soup-15 carbs, a salad- 0 carbs (except for what's in the dressing), a piece of fruit- 15 g carbs.
That's 60 g total carbs, a little lean but enough if you sit at a desk.
By the way, I was normally thin ( BMI 21 to 23) until I was in thirties, and then gradually gained weight. It wasn't until I was forty that I was diagnosed as having hypothyroidism ( very common in middle aged women). Of course the thyroid is under control but ever since then hunger and fat has been a daily fight.
Unfortunately, you are correct. The best defense against obesity is never to become fat. I don't know why doctors don't do thyroid testing routinely on all patients. It's not an expensive test.