Like you say, you know he is only young so that could be a good enough reason.

So, he is only 3 and a half months old... not going to have great control over his bladder at this age. They do say they get "better" control over it once they are about the 6 month age mark... so give it a bit longer. Just keep up with the training and never slip back if you can.

I think taking him out more regularly like you said is a good idea at the moment.

Sometimes things can get worse before they get better if you know what I mean .