Correctol (bisacodyl) is a purgative which tends to increase the contraction of the wall of intestines in order to push the stool downward. It is the cause of the pain that you are suffering from. The pain is likely to be located in your abdomen and not stomach (which is only a small organ within the abdomen). I would suggest a high fibre diet in order to manage your constipation. Please do not take purgatives. Rather take stool softeners or fibre supplements like isabgol at dinner. I understand that other medicines are giving you loose stools but that is what often happens in case of people with constipation. I hope that a high fibre diet will be able to solve your problem. It might still be worthwhile to remain in the follow up of a doctor.