During menstruation there is this chemical that is released called prostaglandins. They are important for the uterine contractions and shedding of the uterine lining. So the cramps one experiences is because of them. They are also the reason for the upset stomach. You can try taking tab. Meftal spas up to thrice daily after food. This may help alleviate your symptoms to some extent. You can also alter your diet during menstruation to include high fibre foods and salads and avoid spicy foods and tea coffee.