First of all it can be due to metrorrhagia which causes uterine bleeding at irregular intervals, particularly between
the expected menstrual periods
. Metrorrhagia can occur due to dysfunction uterine bleeding
, hormonal imbalance, polyps, fibroids, endometriosis, infections of the cervix, vagina or endometrium, pelvic inflammatory disease, ovarian insufficiency, ovarian cysts or benign lesions of the female reproductive system.