I agree a vet visit first. Secondly, any stress or anything different can cause dogs to behave differently and housetraining can often be one of the first things to go :)
Adolescent dogs do sometimes have a setback in housetraining as well, hopefully it is something that can be easily cleared up. Don't tell him off over it, as he may then start to be concerned about going in front of you when he's meant to, and what you'll then get is a dog who waits until the owners have gone and then goes!

Not saying you would tell him off but plenty do as it's a natural reaction although not a good one for training and improving housetraining ;)
Good luck,
Lindsay
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