Spontaneous death (?) of my Pixie Frog (pictures included)

[elastic lizard]

Lately, I've been having very bad luck with my frogs. Over the summer I lost my two Dumpy's Tree Frogs when I had my friend watch over them. He didn't realize they needed a water source and only sprayed the enclosure twice a day... Next, my tiny Green Tree Frog stopped eating and then died of starvation. After that, my Pac-man Frog who was healthy for 6 years died out of no where, pretty similar to what has happened to my Pixie Frog. Now, my Pixie Frog, hasn't eaten in about 3 days and he started to look a littler weaker than normal, by day 2 he was in the water and his hind legs were shedding. I figured he wasn't eating because of this. Today I checked up on him and he was completely still in the water, he felt slightly cold and did not respond to my handling. I want to know what I did wrong even if I'm probably never going to own another frog again.