Did people in the medieval times poop as frequently as we do today?

I can shed a tiny bit of light on this question. Medical beliefs during the medieval era were based on ancient Greek and Roman texts, which designated illnesses to the four humours, blood, yellow bile, black bile, and phlegm. I'm sure you're familiar with blood letting as a medical practice, and this was to purge someone who might have symptoms indicating an excess of blood. Along with blood-letting, enemas (also called glisters or clysters), as well as emetics for vomiting were frequently administered to patients.

Enemas were very highly regarded as a curative measure, as well as a preventative measure for good general health. There's a wealth of information in primary sources and art that shows just how popular enemas were and the openness in which people discussed their bowel movements or lack thereof. Enemas could be simple water, but were usually bizarre concoctions of herbs, animal blood, mercury, and other weird things in various blends that were often held in secret by the quack doctors that prescribed them. Many of them ended up killing the patient by entering the incredibly porous colon and large intestine to enter the bloodstream, though the patient became a pooping machine and visibly seemed to be expelling the excessive humours successfully.

Galen, the ancient author of the most widely used physicians text, was held in high regard until the 17th-18th centuries and the practice of enemas and emetics continued to be popular even into the 1950's and 1960's. Red rubber enema bags were a staple in many American bathrooms, just as Castor Oil was often used as an emetic or purgative when Baby Boomer children had simple tummy aches.

The practice of colonics has reemerged in more holistic and Ayurvedic medical practices in modern times, which indicates that the practice may actually hold some water and not be entirely full of shit.