During menstruation, a woman's body produces a hormone called prostaglandin that causes many menstrual symptoms, including cramps due to the contraction of the uterine muscles, states WebMD. More severe cramping may indicate that a woman's body produces more prostaglandin or that she is particularly sensitive to the hormone.
Some women who experience particularly painful cramping or whose cramps have grown more severe over time may have secondary physical causes for their cramping. Some physical causes of more severe cramping include endometriosis, ovarian cysts and pelvic infections, such as those caused by STDs, explains WebMD. WebMD advises women to see a doctor if they experience severe cramping or if their cramps continue for more than three days.