"Why" is never a simple question when it comes to eating disorders. Eating disorders have many causes, some of them related to ideas and feelings about food and body weight, some of them having to do with other feelings and moods and ideas. What is important right now is not "why" so much as getting help. Neither bulimia or compulsive overeating are manifested with low body weight. Most bulimics have normal weight or a bit over. You need to get a referral to a doctor or therapist who works with eating disorders so they will know how to help you. All of these behaviors are symptoms of an eating disorder, even if they seem very different, they are different sides of the same coin. You haven't been doing it very long which increases your chances of getting into recovery. So go ahead and find some help. You don't have to continue suffering this way.
I was a normal weight when I sought help, and it is frustrating when the therapist or doctor does not think you have a problem, I went to a few different therapists until I finally found one that specialized in food issues. One tool that really helped me was my therapist had me start a journal. Every time that I caught myself in a binge, I would have to stop and journal about what I was feeling at that moment and what I was thinking about or doing before the binge started. Then if I still wanted to binge and purge, it was a conscious decision, and I could give myself permission to do it if that is what I really wanted. This helped me realize I was in control and I could choose to stop...which I eventually did. It helped me uncover that I was focusing on food/binging/purging/starving to avoid having to face fears and struggles I had in other areas of my life. It was a long process, but with the help of a therapist I am now 10 years free of binging, purging and starving myself. I encourage you to not give up on finding help.
The Eating disorder has nothing to do with Your weight it should not go on Your current weight, overweight people and people at a normal weight can be anorexic and bulimic and have other eating disorders while someone underweight can experience overeating. I understand what You're saying about doctors sometimes not knowing it but it is not right perhaps try finding a therapist You're able to talk to who recognizes the problems You're having.
As You would know suffering Anorexia is horrible and the longer You let yourself do it the harder it gets as time slips away so does your thoughts of ever wanting to eat again. You need help now before You get into that category again.
thank you so much for your comments, its hard at the moment i just cant seem to stop eating i am starting to gain all the weiht i had once lost and i am petrified of returning to my old weight or even worse putting more on. the more i try to cut the foods that trigger these binges the more i want them, its like the thought of going on a diet now scares me. my weight issues/ problems seem to be going from one extreme to another.i have had enough now.
You are more than welcome, feel free to message me anytime if You need someone to talk to. I understand your fears Hunni, I really do and I am "Sorry" you are going through this. You have to remember it is Your "inner beauty" that makes you a beautiful person