So i just bought this game and I cant seem to get the dlc pls help

The DLC is in-built to the Game of the Century Edition. If you go into your wardrobe or garage and list the items you have there, you'll see some items which have a fleur-de-lis next to them. That means they are DLC content.

Since im not getting the dlc weapons is it because im at the beginning of the game?

Depends. Did you pass the part in the White Hou... White Crib?