Various factors causing it are endometriosis,ectopic pregnancy,hormone imbalance,endometrial hyperplasia,polyps,use of IUD’s
and depo shots, sexually transmitted diseases,PCOS
and benign
and malignant pathologies of the uterus.
I would suggest you to consult a gynecologist and get a pelvic examination, hormone panel, ultrasound and swab culture done to confirm the diagnosis. Treatment depends on the confirmation of diagnosis.