10-12 x body weight for fat loss is the standard formula used in fitness/figure/body building, based upon slower fat loss for muscle preservation. It's a common formula used in magazines such as Oxygen or Muscle & Fitness Hers. Now, most women using those formulas and looking to lose fat while preserving all muscle mass don't weigh around 300lbs ~ maybe they are around 150lbs. For them, that would be 1500-1800 calories, which is a less shocking number for people to see. But OP is not 150lbs, she is 300lbs, so the number goes up.

I know it can seem like a huge number to the average person, but slow dieting while preserving muscle mass may be preferable to faster dieting with a more substantial muscle loss. Either way, numbers are not set in stone. That's for OP to decide.

I generally go by this guide from Emma-Leigh, who is a doctor that specializes in nutrition:
http://forum.bodybuilding.com/showth...hp?t=121703921

But you are right that the OP should research the suggestion. Anyone should research before making such dramatic lifestyle changes. I promise my own suggestion is based off years of my own research (including into the credentials of the person whose link I posted to). A suggestion is just that, a suggestion.

Ah, you mention tea... Sweetened or unsweetened? How many grams of sugar are you getting a day?

Many people don't seem to realize this, but all carbs are not created equal. Everyone is different, but whole grains are generally fine, and can be an excellent source of fiber. It should not be a main source, but a whole grain bread, low in cal, used to make a sandwhich is healthy for most people. White bread and sugar are not. When I cut out my rice krispie treat (100cal) from lunch, I stopped feeling like napping in the afternoon.

Extreme tiredness can be a sign of many things but the most obvious would be that you're either not getting enough food (energy), or suffering from either a caffeine or sugar (or carb, since processed carbs = sugar) crash. It may also mean you just started running marathons, but I assume you would have filled us in on that.

Since there are medical reasons as well, I would wait another week, maybe make a change or two, but if it doesn't get any better, see a doctor. Just to be safe.