Oh dear, what a question to be asked by someone self titled as Operation_filth. Considering the history of menstruation and the ideas of uncleanness that have often accompanied it the name is unfortunate.

To get you started I recommend you check out the FAQ - How did women deal with menstruation?

There is always much more to be added to the conversation. Further responses are encouraged.

In her book entitled "America's Women: 400 Years of Dolls, Drudges, Helpmates, and Heroines", Gail Collins talks about Native American women using mosses or other absorbent natural substances in a sling to catch blood. She also specifies that in the 1800s, women used spare pieces of cloth that they would later trade out and wash. I imagine it must have been something similar for medieval folks.

It should be noted, lest I mislead anyone, that Gail Collins is not a historian. However, she does include her references at the back of the book.