Sister, Maiden, Monster by Lucy A. Snyder

A deadly virus with stomach flu like symptoms but deadlier, ravages the country. This virus makes some people have zombie like tendencies.
One person transforms into a tentacled monster.
Another is a courtesan who has to shoot one of her customers because he’s transformed into a monster in front of her. She becomes educated by eating the brains of doctors and scientists and watches over the monsters.
The last main character becomes a breeding ground for tentacled creatures that will soon occupy Earth.
Weird, creepy, scary, gross, vulgar and in-your-face horror!