Question..?¿

So I got my period one day late(2/21/19) and lasted about two days(2/22-2/23), followed by sporting twice a day two more days(2/24-2/25) .... the next day before bed I felt a small cramp on lower abdomen ... to find out a very very dark almost black blood in a very sticky form ... I'm anxious about the possibilities of this cause .. help!