Well the first thing I think to focus on would not be gaining weight, but on your thoughts and feelings towards your body. The rest will come later.

Do you have a dr you can talk to about this? I got treatment by talking to my psychiatrist about it. But you can also talk to a family dr, therapist, if you are in school a counsellor or teacher you trust. That's a place to start. It's hard to ask for help, but in the end it is worth it. And the sooner the better.

You need to get help before things get beyond your control if they already are not. I know it's scary, I was scared to get help too, for the same reason ... Afraid to gain weight. It can be a deadly illness and steal your life if you don't do something to get help.

(((hugs)))