If your uterus is doing all the work during your period, why does your back hurt, too? After all, it’s the uterus that’s contracting and working hard to clear out the uterine lining it no longer needs. So shouldn’t it just be our uterus that hurts with every uterine contraction? While this makes sense in theory, a little research shows that prostaglandin changes likely control cramping (either in your lower abdomen or back).
Prostaglandins are the hormones that cause the uterus to contract so it can shed its lining. However, your back muscles may also respond to increased prostaglandins by cramping up just like your uterus.
Usually, back cramping related to your period occurs within the first six days of menstrual bleeding. More rarely, you might experience back cramping as a result of premenstrual syndrome (also known as PMS), which refers to the unpleasant symptoms that occur before your period starts. If your back pain happens in the days preceding your period and you also experience headaches, breast tenderness, irritability, and bloating, you may be experiencing PMS symptoms.