There are several homeopathic medicines which will stop menstrual cramping for most women within a few moments. The key is to know which one to use.
For most women, most of the time, the remedy Cimicifuga will work well. Cimicifuga is characterized by depression, pain in the thighs, pain across the pelvis, from hip to hip, with backache, ovarian pain, and often facial blemishes in young woman.
The remedy Sepia is characterized by indifference and irritability with loved ones, aversion to family or work, and often with tears. There is a sense of pressure in the pelvis. Menses may be late. The pain is often of a stitching character.
Pulsatilla is characterized by discouragement, weepiness, and the desire to friends or family consolation. Menses may be suppressed or late, often after emotional disturbance. There is usually pain in the back, and crampiness in the center of the pelvis.
Mag. phos. is characterized by crampiness which is more spasmodic, and made better by curling up with a hot water bottle or heating pad against the pelvis. Menses tend to be early. There may be a cramping pain inthe ovaries as well.
I would recommend the 6th, 12th, or 30th potency, repeated as necessary.