i know exactly what you're going through
i've got my GCSEs coming up and i'm goin through the a very similar thing!
first thing you should do is go out and get yourself carrots! no carrot sticks or any other form, just plain old, simple carrots! or celery. same thing!
have you heard of negative calories?if not, then they're what you call your body burning more than it gains and there are more foods that do the same thing but i forgot the rest.
so basically, get the carrots/celery and try eating those! with the fact that ur body is burning more than it gains, you should be able to down these because they're not fattening!
after you get used to eating these, move on to another food you think you'll be able to eat and try eating that. ideally, this new food should be in a different food group, but if you're unable to cope with that, then stick to the veggies until you can
if possible, have multi-vitamins! god knows we (people who suffer from anorexia in particular) need them!
if you need anyone to talk to, feel free to send me a message, i know what your going through and i'd be happy to help, read a rant or anything!
it's especially bad when your around our age because we're at that stage where ''no one understands us'' but its worse when you suffer from an eating disorder because that's when you really know that no one understands us [people who have EDs]!