How old was he when you got him? Any past history on behavior/when he was separated from his litter? Sounds like he is bored and extremely under stimulated. You need to take him to a training class and start working on basic obedience ASAP. Also, start investing in some puzzle toys. Kong are a good place to start. There are also things like the Buster Cube and Squirrel Buddy that are good ways to give him his meals that will help stimulate him mentally.
Leerburg has a good article that will give you some insight into mouthing/play biting and how to deal with it and redirect him.
How much exercise does he get? Doe he tug? Does he play fetch/frisbee? Do you walk the same route or go to new/different places? Do you have a crate for him?