Barrier of "tumult" during meditation
I won't try to guess exactly what you're experiencing, but one thing that trips people up a lot is the expectation that meditation is a one-way road to greater and greater calm. In reality, there's an initial calming, followed by the emergence of various kinds of experiences at other layers of the mind, some of which are pleasant or orderly, some of which aren't.

One thing that Buddhism teaches is that the mind is a sixth sense alongside vision, hearing, touch, taste, and smell. This means that thoughts and mental imagery are on the same level as sights and sounds- they are data that enters through "your" doors of perception from "outside". They don't belong to you and are largely out of your control. 

This is contrary to our usual Cartesian model of thinking that our Thoughts are the expression of our core Self, and it's also contrary to the common idea of meditation as the conscious quieting of all thoughts. 

I only have my own experience to go on, but I believe that the ability to achieve a complete stilling of the roiling, random soup of images in our minds is very very rare, if it exists at all, and not a requisite for good practice.