Why are puppies aggressive?

my puppy is 8-9 weeks old, and hes starting to bark a lot, and going under the beds. we try to get him out from the beds but when we try to grave him, he starts to bark and bite us....what could i do in this situation...i try not to hit him because i dont have the heart to do it...so plz any ideas??? we try to use a toy && have him try to chase it (so he can get out of the bed)...we just want him to stop doing that...(being aggressive) =[....plz help