I lost over 100lbs in just a few months, but no one, not even my doctor, questioned my eating habits because I still wasn't under weight. Does this mean I don't have an eating disorder because I'm not sick enough to be underweight?

No, not at all. Weight can be an indicator of disordered eating but it is not the only one. Just because you are not underweight it does not mean that the disorder is not having a serious effect on your mental, physical and emotional well being. It is possible to look healthy but actually be quite sick. Loosing so much weight in such a short space of time is concerning. I had a similar experience where my concerns were overlooked because I didn't fit the profile and I had to keep pushing to get the help I needed, even though I felt unsure and uneasy about it all.

Having an eating disorder is not based on whether you feel sick or not. You know your own body best and you know that your eating habits are out of the norm and you might even need help. That's good! Recognizing you need help is one of the first steps on the path to recovery. Even if your doctor hasn't said anything, you need to bring it up with them. Voice your concerns about your body and eating habits and try to actively seek help changing them into healthier alternatives. You don't need to reach any qualifications to consider getting help, all you need is support and love to battle your demons.