Issues related to attention, concentration, low mood or racing thoughts in young people like you is usually secondary to some stress or anxiety or depression kind of problems. These experiences are fairly common and can easily be dealt with using some psychological techniques and lifestyle modifications, unless it's severe, when you nay need medical help
Next Steps
Now that you are aware of these issues, try and get the context right. Every emotion, thought feeling or behavior has a context and once we get the context right, it all starts to make sense. Once it all becomes understandable, then you have the power to deal with it the way you like, very objectively. Start becoming mindful of your emotions and thoughts all the time and keep noticing the impact while you make attempts to master the techniques of carrying on with your daily routine irrespective of how you feel, so much so that all the negative emotions or cognitive issues loses their significance and disappear. Of course deal with any underlying issues with practical measures without fighting with your emotions