Lower back pain during your period, or primary dysmenorrhea, is caused by contractions in the uterus. Every month your body builds up a thick uterine lining (called endometrium) in preparation for a fertilised egg. If you don't become pregnant, estrogen and progesterone levels drop and cue your body to break down and detach the lining, and it does that by contracting. If your uterus contracts too strongly, it can press on nearby blood vessels, cutting off the supply of oxygen to the nearby muscles, which is the reason pain occurs in the abdomen and radiates to the lower back and even to the thighs.
Chances are, if you've always had similar menstrual discomfort, it's nothing to worry about. But see a doctor if you're incapacitated for more than a few days a month or if you've noticed a sudden change in your symptoms. Meanwhile, you can ease the back or period pain with our dedicated pain relief cream, Soodox for Women available here. Also, you can try a warm bath or a heating pad. Avoiding foods that contain caffeine and salt can also help. And even though you have about as much energy as it takes to plop onto the couch, women who exercise regularly often experience less menstrual pain, so keep up with your routine by doing some light cardio or cramp-relieving yoga poses.