Why is the scaling point not in the middle of my selection? When I'm modelling, why does this happen? When I want the two faces to scale in the middle, the point from where the scaling happens is on one side, so when I scale it becomes weird.
You can select from which origin point to apply the scale using transform pivot points. They are at the top of your 3D view. 

Right now I can see that your transform pivot point is set to "active element" which means you are scaling relatively to the center of the left face.

I am not sure what exactly you are trying to achieve but I suggest using "individual origins".