They don't shed or poop on a schedule. When they're young they shed more often, and poop less. They absorb as much of their meals as they can, and grow. As they age, they still absorb some of the meals, but they shed less often... Mine haven't shed in about 2 months or so. It all depends on the snake. Mine typically poop every other week or so.
Sometimes if they go into a shed and haven't pooped in a while, you'll wake up to a nice clean shed, and lotsa poop and pee.