Endometritis or Infection: This is a common cause of vaginal bleeding 6 weeks postpartum, often resulting from an infection of the uterus that can occur after childbirth, especially if there were complications during delivery or if instruments were used during the delivery process.

Retained Products of Conception (RPOC): Pieces of the placenta or fetus that remain in the uterus after delivery can cause bleeding as the body tries to expel them.
Uterine Atony: Although more common immediately postpartum, uterine atony (where the uterus fails to contract down effectively) can sometimes present later if there's a delay in the uterus returning to its pre-pregnancy size and state.
Hormonal Changes: As hormone levels adjust postpartum, some women may experience irregular bleeding or spotting.

Postpartum Hemorrhage (PPH) Due to Uterine Rupture or Other Causes: Although less common at 6 weeks, a severe hemorrhage can occur due to various reasons such as uterine rupture (especially in women with a previous uterine scar) and requires immediate medical attention.
Malignancy: Though rare, any postpartum bleeding could potentially be a sign of a malignancy such as choriocarcinoma, especially if accompanied by other symptoms like abnormal uterine enlargement or systemic symptoms.
Thrombocytopenia or Coagulopathy: Conditions affecting blood clotting can lead to significant bleeding and are critical to identify and treat promptly.

Arteriovenous Malformation (AVM): A rare condition where there's an abnormal connection between arteries and veins, which can cause bleeding.
Uterine Artery Pseudoaneurysm: A rare complication that can occur after childbirth, leading to delayed postpartum hemorrhage.
Invasive Placenta: Conditions like placenta accreta, increta, or percreta, where the placenta abnormally invades the uterine wall, can cause severe bleeding, although these are typically identified and managed before 6 weeks postpartum.