Sadly, diet drinks (diet soda, coke zero, pepsi zero and the zero calorie monster) use this artificial sweetener which acts as a sort of anti-anti-fat. It prevents you from burning up calories from fat, so you might as well be drinking the real thing. Try switching to green tea, water, black coffee.
---------- Post added 2012-03-27 at 08:24 PM ----------
Even in the best of diets, they should allow 1 or 2 cheat meals a week. Not to say go crazy and eat 3 pizzas in one meal, but if you want a pizza, you can eat a few pieces. If you want a burger, you can eat a burger. But it's 1 or 2 meals a week, not a full on cheat DAY.
I started a diet around November, I cut out fast food, I cut out soda, I cut my portions. I lost 15 pounds in 2 weeks while working out twice a week. (I burned about 1500 calories per work out)
I hit a plateau after those 15 pounds, and then I stopped the diet, didn't gain any weight back. I started the diet back up 2 weeks later, lost another 8 pounds. I wasn't big, but I'm cutting weight down to get really lean and for boxing. (that's the workout i do)
I'm also studying to become a personal trainer, and will be able to work out quite a bit soon! Unfortunately I haven't been able to work out much lately, car troubles, but I'll be back and drop the last 7 pounds while toning like crazy.