Why can't I lose weight?

I am 5'6" and 210 pounds. I have tried a variety of diets. The only one that worked at all was Atkins, but I only lost about 10 pounds then stopped losing (I am sure this was all water weight as well) I drink a lot of water. I don't eat anything with sugar. I don't eat junk food (candy, chips etc) I have never been a huge junk food eater. I would eat it ocasionally (ie maybe once a week) but I have completely cut it out and not missed it at all. I dont eat anything with artificial sweetners. I walk about an hour a night, 6 days a week. About 3 years ago I had my thyroid tested and the doctor said it was fine. I hate going to the doctor and haven't been since then because he always just says I am eating too much and being lazy, which is completely untrue. I am so frustrated. Any suggestions?