Now I am just trying to make a point here, which I believe is factual, although I haven’t heard this from any wo/man, or read from any book, but it makes sense to me, and so here goes:
Of course, your period is caused by the endometrial cell buildup in the uterus, brought about by your hormones creating a proper environment for implantation of a “fertilized” ovum, which took place in the Fallopian tubes [you have two, and so in either one or the other was the egg/ovum fertilized], and therefore due to the hormone output, the body begins not only to create proper environment, but also taps you on the shoulder, making you prepare in other ways for an impending pregnancy. Eating more food in general [which would be needful for the sustenance of the baby—the extra one aboard], or the hormone output giving you a desire for a certain taste/kind of food, would mean the same: more food, and possibly also of a different type only during those days, all occur just before your period begins. Your period is your body telling you you’ve not had a “fertilized” ovum, and therefore there’s no need for the new environment, and so these cells in the form of bleeding, begin to leave quietly enough, but many women have grievous aches and cramping during these days, until the period is over. The uterus actually helps the evacuation of the uterus by small contractions which give a time of from two to five days as the norm for most menstrual periods.
And so a recap: new life, and therefore more food; hormone activity causes you to eat certain foods that are only really desired before and during the period, both of which can answer the increase in feces being caused by increase in intake of foods.
Also, if your doctor gives you a pain medication for severe cramping, if it is a narcotic, it will cause constipation, due to the stoppage of the wave movement of the bowel, as it moves its cargo down and out of the rectum. If the initial cramping gets worse and then finally becomes relieved, you would stop the “codeine” [let us say] usage, for the cramping pains have subsided. Of course when you’ve stopped the usage of the narcotic, it only takes about a half day, and suddenly you are running to the bathroom, because the normal wave movements have begun again a number of hours after you would usually take another codeine, and having possibly had three or four days without regular bowel movements, suddenly all arrives at about the same time. Take your pick of these, but among the three, at least one of them is your reason, I am prepared to stand on. Hope this helps, and if you are needing real help and to be sure so that you’ve no worries, see your doctor, or call a real doctor on the radio—it’s cheaper.