What causes spotting 2 days after a period has left completely?

DUB NEEDS EVAL. DUB (Dysfunctional Uterine Bleeding) is relatively common but needs an eval. Blood work including thyroid and hormonal studies. Also an abdominal and pelvic ultrasound to evaluate for fibroids and adenomyosis. You also need to be screened for anemia and may benefit from iron supplements.