I'm like you, except I have hypothyroidism. I was lethargic, gaining weight and would need a nap when I got home from work. I honestly thought I was dying, so went to my doctor - he ran some blood work and told me my TSH level was 7something, whereas normally it should be 1-3. He placed me on Synthroid and I left the office with a month's worth.
I took that stuff for exactly three days and that was the worst I've felt in my life. I was groggy, even more tired and felt like I'd eaten a bunch of xanax (only thing I can compare it to). The third day I had to pull over and take a nap on my drive home from work, I was so tired. I got home and threw that shit in the trash and never looked back.
That was 3 years ago and since then I've just adjusted my lifestyle similarly to yours. I limit myself to <1500 calories a day, I jog 1-3 miles in the morning, hit the gym after work and go for a 3-5 mile walk with my dog every evening. I also severly limit my carbs (20-30g/day) and eat primarily fruit/vegetables/chicken/fish. I doubt I'll ever cure myself and admittedly there are days when I have to force myself to work out, but I do it. After 3 years, I've yet to get my blood checked again, but my weight has stabilized and I'm 6'-2" and 185 lbs. I go ONE DAY without working out, or slip up and have a splurge day and I'll gain 4-5 lbs, crash, feel miserable and even more tired.
Like you said, I also don't blame people that have conditions like that and just say fuck it. Then again, people that are healthy, have normal metabolisms and are just lazy and push themselves into sickness drive me crazy. To me, I do enjoy parts of my workouts (my walks with my dog, alone time in the gym), but if I was naturally thin there's no way I'd commit myself to my lifestyle. But, I admit that I am somewhat vain and care about my appearance - for better or worse.
My best friend is 6'-4" and weighs about 160 lbs. He hates himself because he cannot gain weight. He eats like a horse, has tried weight gainers and everything else and stays like a string bean. It drives him crazy, but I'm so envious.
The grass is always greener, I guess...