Perhaps taking vitamin supplements could help. It may be from a slower metabolism. Sometimes when you start eating much less than your body is used to, it goes in to panic mode and holds on to all of the fat and calories from the food you eat. All the B vitamins help with energy metabolism. There may be others beneficial to you as well.
Another possibility is you are not burning enough of the calories that you are eating. You may be burning just enough to STAY at the weight you are now. The key is to exercise enough to burn the amount of calories you are eating, or at least a good portion of them. For example, if you are eating 1400 calories per day, you should be exercising enough to burn at least 500 in order to start seeing a difference.
Hope this helps.
Calories have little to do with weight -- it's how you digest and metabolize what you're eating that determines weight gain from food. You could list your diet here, but you'd do better to see a holistic nutritionist to evaluate what you're eating in a more sophisticated way than mere calorie intake.