Free - that really does sound like your metabolism has adjusted to the lower calories. I think you have taught your body to not want any more - but your BMR means your body needs more than you are eating just to stay alive - and thats without any kind of activity at all.
I wish I had your appetite - it must be me... I find it absolutely no problem to get through 1500 cals a day!

I could probably get through double that without a problem....
I'm not a nutritionist but most of the articles/books I read all seem to recommend the following:
A substantial breakfast with dairy/protein, carbs and fruit (mine is about 400 cals)
A mid morning fruit snack (50 cals)
Lunch with carbs, protein and veggies (400 cals)
A mid afternoon fruit snack (50 cals)
Dinner which should be mainly veggies with protein and not so many (if any) carbs. (500 to 600 cals)
You should aim to have at least three portions of dairy a day - especially at your age - to ensure you don't get brittle bones as you get older. Also there has been
research showing that low fat dairy helps your body get rid of fat.
Rosemary Conley says to have a 100 calorie treat each day and a 100 calorie glass of wine - but both wine and treat are optional.
Good luck!