Cramps are caused by the contraction of your uterus during menstruation. It usually means that the uterine muscles are contracting too hard or too fast. You may feel the cramps in your abdomen, in your back, or even down your legs. Try using an over the counter pain killer with Ibuprofen as the active ingredient. Take it the night before you think your period will start. You may also try taking a warm bath or placing a hot water bottle on your abdomen. Some girls feel that mild exercise helps relieve menstrual pain. If the pain still is not managed with this medication, then I think you need to see your doctor. Ask mom to make an appointment.