You probably weren't fired for not picking up your pay checks but because you went awol for 2 weeks with out telling any one or with out giving the manager a reason while you were away. When you don't show up for work then you leave management in a lurch to find other people to cover for you. 2 weeks is usually the allowed time for vacation, if you don't come back by the time you're supposed to with out explanation then you could be fired.
If you're still on good terms with the manager then ask the manager how to go about retrieving your missing pay checks. Usually if you're fired or quit your job any money that is owed to you is sent to the address you filled out on the form when they hired you.