if you not on any medication maybe try some herbs. I'm a herbalist and as well I know the feeling of my mind racing way to fast to concentrate on anything. One thing I could suggest is trying some passionflower or L-theanine and see if that works. It really helps with racing thoughts and calms you down. Try it when you have some free time an have nothing to worry about.

If that doesn't work than maybe you have classical ADHD, something that's slightly sedating will make some things worse. So when/if you try passionflower/L-theanine sit with yourself and examine how you feel with your racing thoughts.

If those make things worse try something that's the opposite like coffee of caffeinated tea. There's many different types of ADHD and many different things that fall under that umbrella term. Classical ADHD is where stimulants help you focus and calm you down, that's probably what kind of medication you would be taking if you where to do so. I know that seams paradoxical but I'll try to explain why stimulants work to calm in some cases.

Classical ADHD has a great analogy for how it works; imagine a traffic cop directing traffic, now that cop falls asleep or is drowsy to the point where he is messing up his job. The cars he is supposed to be directing probably will start to be erratic in their behaviour and try to direct themselves in a more chaotic manor. If you give the traffic cop coffee and he wakes up he will be able to direct traffic again and bring it back to normal. Now think of the traffic as your thoughts and think of the traffic cop as the part of your brain that monitors your thoughts and puts them into order.

Hopefully you can find some use from my post, good luck with your situation and I hope you find something that works for you