shit food like you call it is engineered to be addictive, therefore you crave it.
The shit food industry has perfected the right combination of salt/sugar/fat/texture to appeal to your subconscious and make you addicted to it.
If you want to read about the science behind it in readable book for, this is an eye opening book: http://www.amazon.com/Waistland-evolutionary-Weight-Fitness-Crisis-ebook/dp/B000W7KNDK/
Without knowing exactly what is that you are eating, I would go out on a limb that you're eating mostly ready-made foods/meals. So, it's not you, it's the food. It was ~~made~~ engineered to make you want it more and more and more, and then some more. The texture, color, shape, size, proportion of fat/carbs/salt it becomes an addiction.
If you want more, and more eloquent explanation, this is the book for you: http://www.amazon.com/Waistland-evolutionary-Weight-Fitness-Crisis-ebook/dp/B000W7KNDK
The solution? Switch to non-prepared foods and lift heavy regularly following one of the programs in the wiki. You will be eating a lot of food, food that you like the taste (it might take some time to develop your own portfolio of meals), and that make you feel full; build muscle and make you lean.
Boy, I sound like an informercial for Fittit!
But wait! There's more! The babe will be falling for you, 3 every day, 5 on weekends; money back guarantee.
Call now, operators are standing by.
Void where prohibited.
Nuf!