hi
I have had the little white mites on occassions.They seem harmless and cause no problems.I allways change the substrate if I see them and disinfect the vivarium and they seem to vanish!.My pacman harold sometimes buries himself to his eyes and sometimes only half buries himself? He also sits in his water dish for up to two days even though I spray twice a day.Your frog seems ok and does what mine does,my frog also has a varying appetite ,eats sometimes then perhaps eats nothing for days.
If your frog looks fat and healthy then I am sure its ok.
Keith