I've been struggling with staying thin and have been taking laxatives. is that an eating disorder?

Yes,: Using laxatives to control your weight is considered an eating disorder. It doesn't work and it could really make you very sick. At the minimum, you would disrupt the normal functions of the gastrointestinal system, regular bowel movements, but electrolyte imbalances could affect the functioning of many organs; particularly your heart. Please consult your physician for a good hx and pe and tests.