Hello im 39 years old...i have issue an concern about why when my period gorse off..2or3 days later dark brown liquid comes out

Period inconstant: The stopping of flow, and then "2-3 days later" having a "darker liquid" emerge, is usually because of a clot blocking the cervical canal. In mid to late 30's, the amount of estrogen produced by the ovaries is much higher, creating a thicker lining of the uterus, which gives rise to more brisk bleeding, forming clots which cannot always pass immediately through the cervix, which causes the block.