In reply to Game of Conkers:
Difficult to know from afar, and I'm no vet, but here's a couple of thoughts-
If the calories per serving in the other food weren't what he normally gets that might make him quite hungry and agitated. Our Pointer gets pretty naughty and demanding in the hour leading up to his evening meal....
Watch in case he has eaten something that is blocking up his gut (and therefore stopping him absorbing food). Our GSP ate some pants on the Monday and by Friday he was anorexic and very ill (had to have surgery). We were hoping the pants would just come up, or out the other end. It was a big mistake on our part and we would and should have got him straight to the vet.
Maybe it's time to get his nads off? Maybe he's getting to the rebellious teenager stage and needs some wind out his 'sails' (ahem).
If he doesn't settle down I'd def get him to the vets asap.
Good luck!