Your late menstrual bleeding was darker than usual which means that it was in your uterus or near your cervix long enough to oxidize and turn dark. It smells like feces because E. coli bacteria ingest the old blood cells and this produces the fecal smell of your menstrual blood.
If you have any other symptoms e.g. a fever, pain, or large clots in your menstrual period then you should be examined by a gynecologist in person. Otherwise, it is usually nothing to worry about. Once a day for at least 10 minutes, sit in a bathtub filled with warm water mixed with a cupful of white vinegar. This should eventually counteract the malodor from your vagina.