All faces duplicated My character model's faces have somehow been duplicated. If I delete a face, there's still a face there and I need to delete the face again to see the inside of the character. And its not just one area, it's all faces.

I tried opening an earlier version of my model and I can delete the faces normally. What could have happened on why the faces are doubled? And what can I do to remove them (I tried selecting all, then Remove Doubles, but nothing happened)?

EDIT:

I just fuond out that its happening everytime I add and apply a Mirror modifier after having already applied one. But why is it? I already applied a Mirror initially, I want to edit the mesh again so I need to add a Mirror modifier again. The 3rd time added, faces are now quadrupled.
Somewhere along the way, you probably duplicated all faces by accident.  If that were the case, you should be able to delete them all at one time, because they're connected.  Select one of the extra faces and hit ctrl-L.  This selects all geometry that is connected to this face.  Now you can delete it all.