I think I may've messed up bad.

I've been on a 600-800 cal diet for about eight weeks.  I knew about calories, but not what a healthy intake was so I assumed it was okay.   I only learned about two weeks ago, when I joined here, that the minimum you should eat is 1200, but now I'm stuck and I'm not sure what to do.  I've killed my apetite, almost completely.  Today for example, I've only had about 500 cal, and I'm stuffed.  I went to the doctor today, because my mum was concerned that I've lost what I have in such a short time (she doesn't know all personal details) and all they suggested was eat more, when I really am not hungry.  I feel sick easily.  Starting out I didn't mean for this to happen, but now I'm quite sure I've decreased my metabolic rate because even on this amount of calories I barely lose anything/stay the same/gain a pound or so sometimes.  I also have to walk excessively because my parents are far to busy and I can't afford a car, so anything I do get I usually burn.  I know this may be a useless post, but I was wondering if anyone has been through something similar or can relate in any way.  Even the barest of suggestions.  

your going to have to gradually increase your calories daily. try adding wheat germ to your yogurt or flax seed. try putting sunflower seeds in your salads little things like that can add alot of calories. if you increase your portion size daily eventually you will get it yo where you need to. If you drink tea or coffee add some sugar just to get your calories up until you can eat more. you might gain a little bit at first but when your body fixes itself you will begin to lose again. hope this helps.

Eat more calorie-dense foods, that way you can eat more calories without feeling so full. Fry things in butter. Don't use low-fat anything. Start small and in time your stomach will stretch.

I cannot imagine what it would be like to be full on 500 calories a day. I really can't. It's clearly unhealthy to be eating that little.

Are you underweight? (you must be?)

spoonfuls of peanut butter, nuts, and healthy proteins are a good way to start eating small, but being caloric but in a good way... def start gradually working in more energy for your body.. good luck