Having never had the opportunity to interview you in person makes it difficult for me to provide a diagnosis over the Internet. My recommendation would be to have an in-person psychiatric evaluation to determine if you have a mental health disorder. Having said that, it is reasonable to believe that you may have an eating disorder. In addition to an eating disorder, you may also have OCD.
It makes sense that eating disorders and OCD would co-occur. Both disorders are fundamentally about control. Symptoms of eating disorders and OCD are external manifestations showing an attempt to gain additional control. The individual is actually losing control because the process to gain control becomes obsessive and eventually denies the individual the freedom to make rational, healthy choices.
Your story is a common one. An individual begins to diet and loses a few pounds. Others begin to notice the weight loss and compliment them. It is reinforcing. They like the compliments and figure “five pounds was good but 15 would be better.” They begin restricting more and eating less. For some people, they lose the weight they want and are able to maintain that weight. For others, they can’t stop. Some have described it as an addiction that overtakes them. Each pound they lose makes them feel better about themselves. It gives them a sense of power and control that they may never have felt before. These are the people who often develop eating disorders. The problem is that no amount of weight loss will ever be able to make them feel “good enough.” They may think “five more pounds and I will feel really good about myself; then I will be happy” but it doesn’t work that way. It is an illusion.
There are other causes of eating disorders and they can be found in the many, many books written specifically on this complex subject.
The reality of your situation is that you are heading down a dangerous path. You’ve lost a significant amount of weight and it doesn’t seem as though you can stop yourself from continuing to engage in destructive weight loss behavior. Eating disorders are very dangerous. People die from eating disorders for a number of reasons but primarily because they starve their bodies of the vital food and nutrients that it needs to function properly. It is imperative that you seek help as soon as possible. The longer that you wait to seek help the more your body will suffer. Please get help. I wish you the best.