Why am I having trouble with weight loss? I am female.

What is your "net"? Weight loss is a very nebulous term; 10 lbs of fat loss but 10 lbs of muscle gain nets you no weight loss but better health. A better measure is size (however it is less precise) or an accurate measure of body fat percentage (underwater weighing or bioelectrical impedance, but not calipers.) type of exercise, diet, metabolism, thyroid function, and medications all play a role with your troubles.
Calories in > out. In order to lose weight, we have to burn more calories than we take in (although avoiding carbs seems to allow us to take in a greater # of calories) resting caloric needs can be estimated by height and activity level; it can also be accurately determined if resting expirered carbon dioxide can be measured. Than, you want to keep your calories in at least 3-400 calories below this.