You might be right to consider a biological vulnerability and inherited trait. I cannot make any online diagnosis, but I am wondering about the "real" causes of your depression, eating disorder and drug abuse. It may be related to a dysfunctional type of "self-medication" to feel less stressed, overwhelmed or exhausted. If your problems started in childhood or adolesence you should consider to see an expert for adhd. Some patients with adhd have a very similar history. I recommend a book called "Add and addiction" by Wendy Richardson.
Do not use phentermine. It may cause severe problems to your health. You might need a psychostimulant medication but you should not do any self-medication with this kind of drugs. Prozac or SSRI may show some benefit, but are only one part of a good treatment concept. You might need a multimodal treatment including psychotherapy, coaching, antidepressant medication, maybe psychostimulants and exercise.
But you need to see a psychiatrist with special knowledge about adhd and comorbid disorders