at the stage your frog is right now you need antibiotics, preferably systemic and specialized, not fish stuff, it is working because it is stronger then melafix, so use it exclusively and watch what is happening. I very strongly suggest to call dr. Frye office and ask for meds, he ships them anywhere in US. his contact info is in a sticky in tree frog section.
do not mix meds, frogs are sensitive to everything and if you use too much of stuff especially for babies it will just weakens them up. make sure it is on papertowels ( not filter) and in proper environment ( temps/humidity), put some kind of plastic leaf or small plant in there too, so a frog could hide and cover all 4 sides of your little tank(shoe box, etc) it will keep stress levels down and as such will help with healing.
meanwhile make sure you quarantine the other 2 and keep their stress levels down as well.
good luck!