Depends on where is the pain. If it's an abdominal pain after menstruation, I've felt that before, don't worry it might be cramp after menstruation (sometimes occured for some people). A few days later, you'd feel better. Try to give a warm compress on your stomach, it'd be a lot better. Or it might be caused by eating spices too much, and it also depends on your eating habit. By the way, if this goes for more than 3 days straight, please visit a doctor. Hope you get well soon.