Many frogs slow down eating during the Winter, even if we keep their tanks parameters stable. If frog pooped, we can cross out impaction, which is a good thing. Since you mentioned the substrate, it should be mixed with dechlorinated water too, until it clumps in fist but does not drip water out.

Have you tried feeding night crawlers or other food? How long is the frog body? Does it look normal or is frog loosing weight. Thank you !