I Need Help !, My Doggie Keeps Barking!! HELP. (:?

okay so i have this pomeranian dog (: , FULL BREED ! , he is NEARLY 5 years old... or 4 or something :L ... BUT anyways... so like i use to live in a house.... and my dog has been in that house for almost his whole life... (3-4 years) , and like i had to move houses... and i moved into units.... and like.. my dog has got a habbit of BARKING all the time when people come.. or knock on the door or just like walk past... and now since we moved to units... hes not aloud to bark.... and i really dont know how to stop him from barking... like at night he WILL NOT STOP GROWLING... its so annoying.. and i cant get any sleep.. PLEASE HELP!!!! i really need him to stop, or else he will have to leave AND I DONT WANT HIM TO!!!... so like.. i need him to stop barking... PLEASE help.!! ASAP