From what I have read it sounds like you have the start of one. I completely understand ehy you are confused because the stereotypical idea of an eating disorder is never eating or throwing up when you do but that isn't even close to the truth.
You obviously have a problem because you keep forcing yourself onto diets, and you can't maintain them but then you try again and again. That kind of obsession to lose weight presents a common symptom often presented with an eating disorder. Another thing you have said is that you don't like your self image. If you don't you instantly feel pressure to make it right and you are going to the extemes to get there.
These diets you keep entering into arent classified as dits but as starving yourself. You consiessly arent giving your body the needed vitamins, proteins and sugars it needs to function properly.
Another concern is that you have thought about purging. If your negative thoughts continue, one day you will give in and you will be sick and then you won't be able to get out the cycle and you will lose control of yourslf.
If you want to lose weight try a proper diet where you still eat healthily but also maintain a steady diet and your body will be able to function properly. Past is a good source of food because it provides lots of energy and if low in fat.
Please take my advice and apply it to your life.
Thankyou and if you would like to talk just email me .x.
Love and best wishes, natalie .x.