Endometritis or Infection: This is a common cause of postpartum bleeding, especially if the bleeding is accompanied by other symptoms such as fever, abdominal pain, or foul odor. The infection can be related to the uterus, cervix, or vaginal vault.

Retained Products of Conception (RPOC): Pieces of the placenta or fetus that remain in the uterus can cause bleeding. This condition is more likely if the bleeding is heavy and if there were complications during delivery.
Uterine Atony: Although more common immediately postpartum, uterine atony can still occur weeks after delivery, especially if there was significant uterine distension or if the uterus has not returned to its pre-pregnancy size.
Hormonal Changes: As the body readjusts postpartum, hormonal fluctuations can lead to irregular bleeding or spotting.

Uterine Rupture or Uterine Dehiscence: Although rare, especially if there were no previous uterine surgeries, this condition can be life-threatening and requires immediate attention.
Malignancy: Rarely, postpartum bleeding can be a sign of a gynecological malignancy, such as choriocarcinoma, especially if the bleeding is persistent and not responding to usual treatments.
Coagulopathy: Disorders of blood clotting can lead to significant postpartum hemorrhage. This includes conditions like disseminated intravascular coagulation (DIC) or inherited coagulopathies.

Arteriovenous Malformation (AVM): A rare condition where there is an abnormal connection between arteries and veins, which can cause bleeding.
Pseudoaneurysm or Arterial Injury: These are rare vascular injuries that can occur during delivery and may present with delayed bleeding.
Invasive Placenta: Conditions like placenta accreta, increta, or percreta, where the placenta abnormally invades the uterine wall, can cause severe bleeding. However, these are typically identified and managed before 4 weeks postpartum.