Baby Leopard Gecko death?

I got a baby leopard gecko from a pet store about a month ago. He was perfectly healthy when we got him. On tuesday I fed him about 3 crickets before bed. When I woke up, none of them had been eaten. I left them in thinking he would be hungry a little later. Then yesterday (thursday) I cleaned his cage for the first time, and none of them had been eaten again. I put them back in their feeder cage thingy, and put my lizard in a tupperware container with paper towels on the bottom and a small hide. I only used hose water to clean the habitat. Then I dried the habitat, put the heating pad, water bowl (full of hose water), and branch back in his cage, and placed him back in. While he was in the tupperware container, he had very green and watery stool. When I placed him back in the cage I noticed he was very sluggish. I woke up today and he had moved to the opposite side of the cage and was not breathing. Then when I touched him he didnt move, and I picked him up and he flipped over. So he's dead now. Do you think it was anything I did wrong, did he die of shock, or was it just the circle of life? No rude comments please, I'm still crying over his death. He was my first reptile. And yes I did read up on leopard geckos before I purchased him.