It sounds like it could be the infamous 'Wall of Death' that young cockers (and some old) are so fond of
. He's the right age for adolescence as well, so could be entering that often tricky teenage stage. It's usually a case of going back to basics with them as they forget how to behave. It does pass, eventually
.
At that age their back teeth begin to set in too, which can cause discomfort, so make sure he has plenty of things he can chew.