Dysfunctional Uterine Bleeding (DUB): This condition is the most common cause of abnormal vaginal bleeding in adolescents. It is often related to anovulatory cycles, which are common in the first few years after menarche. The bleeding is typically heavy and prolonged.

Pregnancy-Related Complications: Although less likely if the patient is not sexually active, pregnancy-related complications such as a miscarriage or an ectopic pregnancy can cause continuous vaginal bleeding.
Infection or Inflammation: Pelvic inflammatory disease (PID), cervicitis, or endometritis can cause abnormal vaginal bleeding.
Hormonal Imbalance: Conditions like polycystic ovary syndrome (PCOS) or thyroid disorders can lead to hormonal imbalances that cause irregular menstrual bleeding.

Malignancy: Although rare, cervical, uterine, or ovarian cancer can present with abnormal vaginal bleeding. It's crucial to rule out these conditions, especially if the bleeding is persistent and unexplained.
Bleeding Disorders: Conditions like von Willebrand disease or other coagulopathies can cause heavy or prolonged menstrual bleeding.
Foreign Body: A retained foreign body in the vagina, such as a tampon, can cause continuous bleeding and infection.

Uterine Anomalies: Congenital anomalies of the uterus, such as a unicornuate uterus or a uterine septum, can cause abnormal vaginal bleeding.
Adenomyosis: A rare condition where tissue similar to the lining of the uterus grows into the uterine walls, leading to heavy and painful periods.
Arteriovenous Malformation (AVM): A rare vascular anomaly that can cause abnormal vaginal bleeding due to the abnormal connection between arteries and veins.