Littledolly,
It sounds like you might need a better doctor who listens to you so you can rule out a medical issue. If you get a clean bill of health, perhaps you might see if your weight loss is a stress reaction. Many people lose weight/forget to eat/etc under stress. The treatment is two-fold: learn to reduce your stress and then learn to deal with the stress.

You're posting this question in an eating disorder forum, so I know you're worried. I hope you can take the next steps to address this issue. Find and see a new doctor, and perhaps see a therapist or counselor who can help you learn more about yourself and overcome this problem before it becomes a big issue.