What could cause random blood clotting without being on your period?

Retained blood: Most clots passed from the vagina are accumulations of small amounts of blood over time, like overnight or caught in a fold of the vagina, before passing, with a patients increased physical activity. The blood may be from "break through uterine bleeding", a lesion or sore on the cervix, or something from the vaginal wall. All abnormal bleeding should be evaluated.