There are two actions to take that will start you on the path to better concentration and less "cloudy thinking" -- both of which I dealt with personally.
The first: reduce the amount of sugar in your diet. If you're like most people, you are probably consuming a whole lot of sugar. The average person consumes 170-plus pounds per year from many different sources, compared to around 7 pounds per year in the late 1800s. Sugar is hidden is a large percentage of the some 350,000 different foods, and is responsible for too many of the health problems we are facing in the US, and seen growing in other nations as well.
It may sound counterintuitive to brain function to drastically reduce your sugar consumption, but as you may quickly deduce, too much of anything starts to have negative consequences. Sugar is no exception. It puts your brain on overload. Many studies suggest that the ADD and ADHD epidemic has more to do with our over-consumption of sugar than any other cause, genetic or otherwise.
Regardless, try it for two weeks. How? Get rid of soft drinks, potato chips, sweets, and most of the foods you find that in a wrapper, box, bag, or in a window (drive-through).
Step 2: Replace what you are reducing/eliminating with the healthy stuff. That means start adding some fruits, vegetables, and berries to your diet. If you can focus on a variety and trying to add just as many vegetables as fruits (50-50), then the benefits will be noticeable and significant.
Now since most of us don't get adequate nutrition from those plant-based sources, I would suggest adding a daily nutritional supplement that covers an array of nutrients, as opposed to one source that many people may say is good for concentration. The truth is you need nutrition from a variety of good sources because it's not just your concentration with which you should be concerned. When your overall health is functioning at its optimal level, you will find your concentration is optimal as well.
Think of it this way: you're only as good as your body's weakest link. If your health is suffering in some other area, it's not as though it is acting on its own. You will be distracted because of it, whether consciously or subconsciously, and therefore your concentration will not be the level you want.
Here's what to look for when choosing that ideal daily nutritional supplement: The product is made using the whole food; it is comprised of mostly (if not all) organic foods; it includes superfoods -- those foods we know to contain relatively very high levels of nutritional content.
The three companies I found that make a product (a daily nutritional supplement) that fits these three criteria are: Barleans, AKEA Essentials and Green SuperFoods by Amazing Grass.
I have personally tried all three, but opted for using the AKEA because I love the taste and the addition of pre- and pro-biotic enzymes and fermented foods, all of which aid in the digestion and health of the intestinal tract.
I had the same problem with "cloudy thinking" and concentration and memory issues, and these two steps and the supplement addition has been a life-saver. Having to read a paragraph over and not having good recall is frustrating when you read close to 100 books a year and you want to remember all the important points. Hope this is helpful.