What trophies were you expecting to have? If you're only just over half way you may get the 'Crafted all items' trophy but most others you shouldn't expect to get until you've almost completed the game (collectables), finished the game or played a second time on Plus (fully upgrade Joel, upgrade all weapons, etc..).
There are only 23 trophies in the game not including platinum, and most of them require you to of collected all of the collectibles or maxed out your attributes and weapons. Aswell as multiplayer trophies and game completion. You wouldn't be expected to have much of any trophies half way through the game.