Well, you should probably have a recheck for parasites...those little buggers can be hard to detect
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We went through a phase with Nisha were she had off and on loose stools...not diarrhea, but 'soft'. She also couldn't keep weight on. Turns out, she had Giardia! It took three fecals to find it
! It can be very hard to detect and can also cause sporadic loose stools. I would have the vet check for that as well.