Here's a list! Pregnancy. Reproductive hormone imbalance. Polycystic ovary syndrome. Thyroid problems. Recently starting or discontinuing hormonal contraceptive. Insertion or removal of an IUD. Uterine fibroids. Pelvic infections. Endometriosis. Vaginal foreign body (for example, tampon.) This list is incomplete! Start with a home pregnancy test, then see your gyno. Best wishes!