Since many others have pointed out what you have been doing wrong, I'll take the opportunity to share a diet that has worked wonders for me and others.
First off, there is nothing terribly wrong with Atkins or the South Beach etc--they work. But are they the most healthy? A diet should not only help one reach optimal weight, but also enhance and strengthen the immune system and help one sleep better, have more energy etc.
I've been on the paleolithic (or hunter-gatherer diet)
for almost six months. The key insight into this diet is that for the vast majority of our evolutionary history as proto-humans and homo sapiens we ate a diet rich in animal protein, vegetables, fruits, nuts and seeds. Eating grains began approximately 10,000 years ago. There is much evidence that many health problems can be traced to this momentus change.
As hunter-gatherers we didn't eat dairy, salt (or certainly not in the quantities humans eat now), refined sugar, fried foods and so forth. We got all our carbs from fruits and veggies. Tons of protein from meat, fish, seeds and nuts.
If one eats as our ancestors did, the benefits will be seen very quickly. I lost 12 pounds in a month and gained muscle mass. I sleep better and I haven't been sick since last year. I gave up beer, but hey,
I'm much more of a wine drinker anyway. Dinners have become easier as we grill a lot more and eat lots of salad and other veggies. If you can afford it, buy clean sources of meat (organic, free-range, hormone free etc.). Eat sunflower seeds, pumpkin seeds, brazil nuts, walnuts. Eating nuts and seeds can significantly lower your risk for certain cancers such as prostate.
The problem with Atkins as I see it, is that not enough attention is paid to eating lots of fruits and vegetables.
This is the stuff that keeps one cancer free and one's plumbing working properly. How healthy can a diet be if you need to buy fiber products? (As many Atkins people do.).
Check out these links:
www.paleolithicdiet.com
www.beyondveg.com