Have you not rotated at ALL?  JUST Ivermectin?  If so.. I'd seriously consider revamping your worming protocol!  Not all types of worms in all stages shows up on the fecal tests, so you can't base your entire program just off the test results.

image"Avoid loud and aggressive persons, they are vexations to the spirit." - Desiderata, Max Ehrman. 1926. image