No need to panic at this point. Has the frog ever been treated for gastrointestinal parasites? That could be part of the problem, if there is a problem. If it doesn't eat by Sunday take it to a vet. If you can bring a fresh fecal sample, no more then 24 hours old.
I think your tempertures are fine, the humity could be higher. Misting the living **** out of the cage should help. And if you change the substrate to sphagnum moss, that will help too as it is pretty good at holding on to moisture.
So in conclusion, my guess is it's either GI parasites and/or too low of a humity. Then again, there may not even be a problem.