Hi! I was always told that the minimum that you can eat and have the energy you need is 1200 calories for a woman. So I always made sure I got at least close to 1200 calories (and by close I mean about 20 calories either over or under)....at least on most days. Some days I couldn't make the 1200 just because I was busy and had to skip a meal. But for the large majority of the time, I at least ate 1200.

Eventually it started becoming easier for me to eat the 1200 calories. I think a lot of my problem for the first couple of months was adjusting to a new style of eating. I kept trying to keep my calories down during the day because that was what I was used to doing, but once I went low carb, I really didn't need to do that. I stopped having to save room for the coca cola and the cookies and the chips and the bread once I stopped eating them.

I fell off the wagon around Christmas and gained 10 lbs. I know exactly what I was doing wrong; eating my yummy low carb things and eating sugar, crackers, etc in addition. Disaster in the calorie department. I started back in earnest last Sunday and have stayed within my calorie and carb goals so far. Toast in the morning is a catalyst for being hungry very soon. You said you don't know what you are doing wrong, but toast for breakfast is your first clue. Do what you already know to do. Protien and fat in the morning, high fat snacks (1/2 an avocado or peanut butter; not primal or any sort of nut butter). It's much easier to stay within your calorie goals when you are satiated but at 800-1000 calories, you must be starving and you just don't have to be.

Please go to the following website for a good estimate of your BMR.
Your BMR is the minimum of calories you should be eating daily.

http://www.fat2fittools.com/tools/bmr/