Sounds like you body is where it needs to be. Don't abuse it. Eat well, but eat enough. Exercise, but don't overdo it. Start loving yourself and your body enough to want to be healthy. You'll feel better, look better, think better.
You should be eating no less than 1200 calories a day. So triple what you're eating. 400 calories a day may lead to rapid weight loss, but what you're losing is water and muscle.