Period cramps.

One of the most hated parts about having a period are cramps. Everyone is different, so some people that you’ll meet may feel little to no pain at all during a period, and some need to take painkillers to numb the pain. Cramps are caused when your uterus contracts to help remove its lining, and releases a hormone called prostaglandins that trigger the pain [1]. People with higher levels of prostaglandins may experience more painful cramps. But you should go see a doctor if the cramping pain becomes unbearable.

[1]: https://www.mayoclinic.org/diseases-conditions/menstrual-cramps/symptoms-causes/syc-20374938#:~:text=During%20your%20menstrual%20period%2C%20your,with%20more%2Dsevere%20menstrual%20cramps.