orange cubes are the worst, i had a very high mortality rate of crickets and my geckos that are fed supplementary with crickets had a very soft stools. fluckers ca is good, but i like natural way: lettuce, carrots, apples, oranges, as a dry foods sometimes i do grind cereal with some spirulina, tropical fish flakes and small percentage of cat food. works for me
try to feed exclusively crickets for a week, you should see the difference in stool consistency, if added just occasionally- not so much.

behavior - if a frog has infection - you will see that something is off, sometimes that something you can't put your finger on but it is off. if it has infection in digestive track - his poop will stink, more then usually and consistency will be runny, not just loose and dissolving in water.

but it is always is better to be safe then sorry, get a sample tested, you'll sleep better at night