Premenstrual syndrome, also called premenstrual tension is a collection of emotional symptoms, with or without physical symptoms, related to a woman’s menstrual cycle. (Wikiepedia)
Your body prepares the uterus for receiving an embryo, and then when it realises no fertilized egg is coming it sloughs off the extra blood and tissue that become your period.
It is the hormones (oestrogen and progesterone) preparing for this event that cause the rise in temperature, expansion of milk ducts and consequent tenderness and swelling in your breasts, the irritability and anxiety, bloating, gas food cravings and finally cramps!
Then your body returns to normal…. until the next month!