I would just go in there and tell him the honest truth. The same thing kind of happened to me, my doctor put me on a diet plan, and I felt like I was seriously dying. I was being starved, and had pains and everything.
I left him and started my own plan.

I use a site called "myfitnesspal.com" to track what I eat and my exercise.
You put your weight, how much you want to lose, and how much you can work out. It will give you a calorie intake, protein, fat, cabs, etc.
I've lost weight on it, and still am, very quickly actually and I'm not that active.
You must stay within the limits it tells you though, or it will not work. I also suggest eating healthier if you don't already do. For breakfast I eat 8 medium strawberry's, 14 baby carrots, and a 90 calorie granola bar, and all of that ads up to 185cal, which is very low compared to other meals, but it's really filling. I thought I was just inform you on this site, since it has worked for many people including myself. And I wish you the best with your weighloss.