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Consider reporting to ER or make an urgent visit to your gynecologist for examination, ultrasound scan to find the cause of the heavy bleeding with clots. If you had been having unprotected intercourse after childbirth, then the heavy bleeding and clots could be suggestive of a miscarriage. If the ultrasound scan done confirms presence of retained products of conception in the uterus, you will need to have a D&C (dilatation and curettage) to clean up the uterus and stop the bleeding.
Take care.