Margins on mobile devices

Almost there, just going crazy on little details, but it's almost over. Only one thing remains, when I tested it on mobile device or zoom in with pc posts gets too thin on the middle of the screen and there's a lot of space by the sides. please, take a look on: http://farma-ceutics.com/category/exercici-fisic/ by zoom or using mobile devices (or screen simulation) and you'll see what I mean. Thanks!!