I think it would be extremely rare for a 9 week old puppy to be aggressive unless there was some serious trauma that went on.
Most likely, it is the teething.
Get yourself some "Bitter Apple" and spray it on your hands, feet, wherever he's biting you- it's almost guaranteed to work
Also, just keep teaching him "no" and re-direct with toys. You can also freeze some toys and have him chew on those. The cold will numb the pain a bit and help with the teething.