Fibroids or Hormonal. Uterine menstrual cramps are due to the release of a substance called Prostaglandins that cause uterine contractions to help expel menstrual tissue/fluid during your period. Hormonal changes or uterine fibroids or polyps can lead to persistent cramping, especially in women over 35yrs old. Try ibuprofen or naproxen. Seek medical attention if ur cramps persist; asap if they worsen.