HOW OLD is this guy??? Constantly walking and not being able to settle is a sign of pain....By this point, it's usually serious pain.....
Since food seems to be involved, I'd have his mouth & teeth checked thoroughly.....Dental disease is common & dangerous if left untreated....Maybe an abcessed tooth or something lodged in mouth....
Has he ever had a dental???
Is it possible he has something stuck in his mouth???
A Vet visit is in order...I wouldn't wait any longer....Please, let us know what you find out....
Okay he may have some health problem going on. This isn't normal for him by the sound of what you say, and if he's only just started acting like that, something may be wrong, especially as he isn't interested in food.
He needs to see the vet.
It is possible this is behavioural....but get his health checked first.