A 26-year-old G2P2 woman underwent a normal vaginal delivery 10 days ago. She comes into the doctor's clinic complaining of a large amount of bright red bleeding beginning since 5 PM the previous day. Which of the following is the most likely diagnosis

The most common cause of late postpaum hemorrhage is subinvolution of the uterus, in which the placental implantation site does not decrease in size as expected; thus, when the eschar overlying the placental site falls off (7- 10 days after delivery), there is more bleeding than expected. The treatment is uterotonic agents such as ergot alkaloids or misoprostol. The bleeding almost always decreases quickly, such as within 12 hours.