You are definitely too low. You should really avoid going under 1200, and you should not be at that level until you are much nearer to your goal.
I would honestly raise your intake to about 1600 a day...and aim for 1-2 pounds lost per week. Once you get to the point where you are no longer losing (a couple of weeks with no loss...) then drop it to 1500 a day, and slightly increase your exercise. (It can either be by adding an extra 5 minutes a day, or raising your weights if you use them, or walking an extra 1/4 mile if you walk for exercise, etc.)
The more you weigh, the more calories you burn during activity. I have explained this in another post-but think of it this way-if a 250 pound woman walks a mile with a woman who weighs 150...the 250 pound woman burns more calories doing it. (She is carrying an extra 100 pounds WITH her all of the time...) This is why when we are overweight, exercise, going up stairs, etc. takes so much more effort!
As you lose weight, your body has less weight to carry around, so we expend less energy to do it...so after losing 15-25 pounds, you might find at 1600 you need to drop your calories to 1500 a day or increase your exercise, and so on and so forth.
If you are in the 240's and are already at 1200 (and you are even lower!!!) then when you hit 200, or 180, and your losses stall-you have nowhere to drop your calories.
Start weight after baby #3: 233.9
Current weight: 143
90 pounds lost!