For help with the body image, do toning excerised and drink plenty of water.
You need to increase your caloric intake to at least 2000. I lot of people are going to jump in and say "OMG EAT 3500 CAL PER DAY NOW!" You dont need to, your BMI is within a healthy range. If you needed to gain weight then yea eat 3500 calories, but you dont need to so slowly increase your caloric intake to 2000.
Although I want to warn you that yes, you will gain weight at first. It might stay for a month it might not. It will be weight from water and food in your digestive tract and possibly new added muscle or fat (that will go off eventually after your body realizes its not starving).
What jumps out at me in this post is you are afraid your eating disorder will develop again. Are you seeing a counselor? That's the most important thing to do. I know this is easier said than done, but at 15 the thing most worth focusing on is your mental health and your education. And what concerns me is that your preoccupation with your weight is causing you discomfort and interfering with your experience at school?
You have your whole life ahead of you! I hate for you to regret all this focus and energy you're paying your physical appearance. Of course health is important and maintaining a healthy weight. But you're just 15 and you've already got all these crazy 'hormones' working against you-- so you just have to relax for now and I guarantee you your body will adjust...
It takes a while to lose weight so I highly suggest you eat healthy (1200 to 1400) per day and do cardio for like an hour everyday when you can. It would take you 6 months to one year to achieve your goal weight. Follow a low sodium diet. Works for me :D