Need some advice about how to lose weight?

Ok, this is weird. I posed this question a month ago, and I got some great answers. Unfortunately, none of those tactics have worked, and I'm still in a rut. I'm a 28-yr-old female, 5'7 and 190lbs. There's lots of muscle on me as well. I tried the South Beach diet for 2 weeks (NEVER cheated), and I exercised in conjunction. No weight loss. Then I switched to Atkins (yes, I know it's a horrible diet but I was desperate). My blood sugar was so low that I actually managed to get into ketosis, which meant that I should have been losing weight. No results. Then I bought hoodia (the pure kind--not that fake crap) and I was still left hungry. What the heck is happening? Two years ago, when I tried all these diets, they actually worked! I saw mad weight loss. I know a person's metabolism changes with age, but mine shouldn't have changed so dramatically in two years that it's virtually impossible for me to lose (other than starvation!). Can anyone help? Are there any nutritionists out there???