The thing with this is that you had starved yourself, when you starve yourself your metabolism slows down because your body doesn't know when it'll get food and nutrients again, so then when you start to eat again it immediately hangs on to what you give it because after starving your body, it doesn't know when it can get food and energy again. That's what sends a lot of people recovering from
ED's into relapse. You just need to eat healthy, you will probably still gain weight but after a while of healthy eating plus exercise it'll regulate out to a good weight again.