Having a period less than 2 weeks apart what can be the cause of this?

Usually irregular: ...periods are caused by irregular hormones. Since the productive hormones are carefully orchestrated, it doesn't take much to upset them. An occasional missed or early period isn't a concern unless it's accompanied by other symptoms (pelvic pain or discharge, tender breasts for example). If you get another early period, contact your gyno. Best wishes. Dr. Anne