Going potty is a vulnerable thing for pups, I get the feeling inside is more comfortable for them. My pup had bad diarrhea when she came home and had to be house bound for two weeks. She would go potty outside only if she had to after that. I'd start from scratch and try not to get to frustrated, big potty parties outside every time. The other thing that helped was sitting calmly outside getting treats every now'n'again, the more comfortable she felt outside the better it got.