Hi Crzyrp,
I am in a similar place to you in that I am terrified of gaining weight.
It can be really hard to eat when you really are wanting to just restrict and stay away from all food, but for your health's sake, you must eat. Absolutely must.
Take a look at Jessee's thread titled "There are Worse things than gaining weight". That scared the crap out of me and reminded me that if I don't eat and continue to restrict, I could be in deep sh*t, so to speak.
I don't know about you, but I come from a family of women who pretty much all have eating disorders (mostly anorexic, some bingers) and one thing that can motivate me to eat is looking at them and seeing how it has damaged their bodies and ruined their skin. Many of my aunts are in their 40's and their ED's have made their skin extra wrinkly and old looking and I do NOT want to loook old.
Try to find negative things, even if they are shallow, and blow them up as motivation to eat.
It could be wrinkles, organ damage, people not finding you as attractive because you have no curves, etc. Whatever works.
Lastly, sadly, you cannot just eat salad and expect to gain weight. You need a balanced, healthy diet made up of more than "rabbit food" as my Dad calls it.

I know it can be scary, but you have to trust your doctors, especially since you have BDD.
Hope this finds you well! Hugs!
Dx:Impulse Control NOS, GAD, BPD Rule-Out.