Now that I'm reading this, it sounds like he may have some health issues. If he hasn't been checked by a vet, that's the best thing to do right now, as soon as you can get him there.

I have Chihuahuas and they were pretty hard to potty train. I stuck with a few papers in the house at first but I later decided to remove them. More than anything, it was fooling me and I was getting lazy in getting them out often enough. I didn't think it was a good long term solution.