Hey Sheila,
At 309 pounds, you should be eating more than 1200 calories a day, even to lose weight! Your resting metabolism even if you are sedentary would be between 2100 and 2500 calories at that weight (I don't know your age, though). You can look up what different websites say by searching for "metabolic rate calculator."
So to lose weight at a pound a week, you would need to eat 500 calories a day less than the resting metabolism level, or burn 500 calories more with exercise. Or, a combination of the two. That means you should probably be eating closer to 1600 calories per day--perhaps more, depending on your exercise.
Which is the long way of saying what lovelypurple said!

That's probably why you are tired.
Jay