How can I repair my metabolism?

I basically killed my metabolism after suffering with an eating disorder for the last 8 years. In an attempt at recovering, I started eating 1200+ calories each day (a huge jump from what I was eating) because the only real way, I thought, to repair my metabolism was to give it more food to work with in hopes it could function and eventually burn/use food effectively. However, it's been over a month and I've only gained weight. I expected some weight gain but was told it would come back down. It hasn't. I'm steadily gaining more weight, and this bothers me because despite my eating disorder, my weight wasn't and isn't low. It's very, very normal and healthy.. but with the weight gain, it might not be soon. Other than healthy eating and exercise, how can I get repair my metabolism and stop this weight gain?