Final answer:
The possible cause of amenorrhea in a 14-year-old female with negative pregnancy tests and amenorrhea for 3 months could be anorexia nervosa.
Step-by-step explanation:
The possible cause of amenorrhea in the case of a 14-year-old female with negative pregnancy tests and amenorrhea for 3 months could be anorexia nervosa. Anorexia nervosa is an eating disorder characterized by consistently eating very little and becoming extremely thin. It can also lead to amenorrhea and other serious health problems. The food restriction in anorexia nervosa can result in excessive weight loss and often amenorrhea in females.