was he ever properly toilet trained? You need to go back to basics I'm afraid. As mentioned before buy some stuff that will neutralise the urine smell so he's not attracted to weeing in the same spot and then most importantly DO NOT LET HIM OUTSIDE AS OFTEN AS HE WANTS because he's not being taught to hold it.
So many people get puppies in the summertime where the pups can run in and out of the house as the garden door/s are usually open. Then come winter and the owners can't understand why their dog wees in the house. Well the dog has been used to running outside to do it and when he get to the door which is now shut, he will do it in the house.
So once you've neutralised wee smells, try and see how long he can hold it. Can he do an hour? 2 hours?. You need to read up on how to toilet train a puppy as that will give lots of tips and advice. With our puppy we started with 1/2hr then outside every 1/2 hour. and with time we slowly progressed. When they have mastered the time you have set you can increase by 1/4 - 1/2 hr and see how you go.
When out give a cue word to when he does a wee so eventually you'll be able to say the cue word and he'll do it for you. and ALWAYS give him a treat for doing it outside. If you have any accidents in doors DO NOT shout at him. You need to keep a watchful eye on him and get him outside if he starts to show signs of wanting to go. If he's already done the wee and you didn't see him doing it, pretend as if nothing has happened and just clean it up. Don't get angry, don't fuss, just don't react in any way to it.
Good luck