Help, my dog is eating EVERYTHING!

my Gordon Setter has been acting very strange lately by eating everything & anything in site! he has been fine until just about 2 months ago...he suddenly started jumping up on my kitchen counter (when we're gone) & eating everything he can reach...whether it's edible or not.... I have had to lately when I leave for work put him in our back entry way.. yesterday I left him for no more than 1 minute.. & he had gone into a small trash can & tore up all the paper & was eating it when I came in.. he also chewed up a t-shirt.. until this started he had 2 other dogs & a cat to play with during the day... they all had the run of the house & lots of toys to play with.. he chews up anything he can get ahold of... when he has to be in the back entry he wines all the time & barks.. he wants attention all the time... I mean ALL the time... does anyone have any ideas as to why this behavior would start? nothing has changed in our lives so it's not like there's a new baby or pet Nothing at all... if you have any ideas PLEASE help... I hate leaving him alone in the entry all day....but he's becoming to destructive during the day.. I forgot...he's 9 years old