In the eighties I published two science fiction books (a novel and sequel) that occurred in a world several generations after all oil and all petroleum products suddenly disappeared. (Long story short--it had to do with a recombinant DNA disaster involving oil-eating bacteria.) The novels follow three protagonists who are devoted to preserving as much from the past as possible, but from a very primitive base. As The Knowledge points out, most modern humans are completely ignorant of basic survival tools. One of the characters, the leader of a fledgling society based in the ruins of Washington, DC, has his hands full just trying to get his people to practice elementary hygiene. Other societies include a group of religious fanatics who are virulently opposed to all "science" (including hygiene) because it was "science" that caused what they call The Change. Another group consists of an enclave of women scientists who are trying desperately to help solve a genetic disease that kills women upon the birth of their second girl-child and threatens to wipe out humanity. Within these settings is a romantic adventure story, featuring a strange love triangle. The books are Pandora's Genes and Pandora's Children, by Kathryn Lance; they are out of print but can be found on Amazon Kindle. I am currently completing the third book in the trilogy.