If you don't think your issues are that bad, perhaps think about the things going on in the back of your mind to see if they are that important. But maybe focus on the present and keep refocusing on the present.
There are other not so obvious reasons but it will take time to get to the real cause of this problem. I suggest you find a good meditation app in the google or apple App Store and follow the very helpful mind calming meditation features and audio presentations. One such site that’s good at doing this is CALM.
Your journey to better your cognitive powers is shared by many others so there are a lot of helpful apps on the market to fit your particular need Use the search line in the App Store and type in app to improve concentration and see what you come up with. Pintrest can also give helpful information when you type in a certain keyword to find out about a topic.
I hope you will be successful in finding your special app, or even e-book or magazine article to get the help you need. Once you start searching for the answer things will begin to make sense as you get farther into your search. I know it’s done that very thing for me.