Jane,

If you're really feeling full at just over 1000 calories/day and don't feel that you can increase the amount of food, maybe you could try and choose more calorically dense foods. That way, you can move closer to your calorie goal without feeling like you're overeating. I think it's really important to eat an adequate amount of calories in order to keep your metabolism fired up. It's like stoking a fire. If you let the fire die down to a glowing ember then your body will conserve energy, whereas if you add some timber and get those flames burning, then your body will feel the freedom to burn more calories.