Fasting puts you in ketosis. Starting Atkins would be a continuation of that ketosis, so you would certainly not gain "fat".

Some people who fast do not have an eating disorder, but your method is a little out of the norm. I almost agree with the visit to the doctor, but a doctor will probably not recommend what you really need, but will prescribe drugs instead.

A good, well educated low carb diet will help you develop a healthy body size, whether you need to gain or lose weight. It can help you overcome the urge to binge-eat and stabilize your metabolism.

Eat whole foods which are low in carbs on a regular basis, and some of your worries about your diet will be settled. I promise.