Hi there, I just found this post, and I do realize its quite some time now since you posted. If you still have the kitten and are still having problems, I also had a problem with a stray kitten I took home once. I found it was the litter that was the problem. I had to fill the box with actual dirt, and then gradually switch over the litter because she was used to doing her business outdoors. Poor thing didn't poop for two days til I figured out why and then she was fine.