Cramps, back pain, headaches. It would be heaven to sit in a hot bath for a week until all this went away but who's got that luxury.  Look for this symbol when picking products for your box.
During your period, the wall of the womb starts to contract vigorously to encourage the womb lining to shed away. This temporarily cuts off the blood supply, and oxygen supply, to your womb. Without oxygen, the tissues in your womb release chemicals that trigger pain. In addition to this, the drop in oestrogen just before your period can cause headaches.