Ebony was 3 before she would ask to go out and even now you get about 2 mins to let her out before she'll go by the back door for a poo!
She was the 1st puppy I house trained without paper indoors and followed to the letter taking her out every time she'd had a play, eaten, or evey 20-30 mins. We got her when there was thick snow,followed by weeks of rain which she loved for playing in and I spent ages with her trying to get her to wee or poo. It became a real battle of wills and I think that was the problem.
However when we went to our caravan she was only too happy to go out and perform, it didn't make sense. In the end I decided she was stressed to go outside at home. In the end I carried on getting her to go out, but didn't go with her and praised her to the hilt when she went. I totally ignored when she went inside, although she still went to the cupboard for a treat
. Eventually there was a lightbulb moment and she worked out she only got a treat for going outside.
Providing there is no underlying medical issue,my only advice is, hang in there, just ignore the messing indoors and go wild with praise and treats when he goes outside. He will get it eventually. Hope it goes well at the vets and that he's just contrary