You can try meditation and yoga for relaxation and improvement in concentration. Whatever you do, start with a peaceful and a clear mind. Focus on your work. Set a time limit, if you're reading something, set a time cap to finish reading that particular topic in under 30 mins. Focus on every detail of your work and more importantly, enjoy what you're doing. When you enjoy, your mind won't wander off
What kind of thoughts have you been experiencing?
Do you know about intrusive thoughts? You might be experiencing those which can be very difficult to deal with. I hope you get all the help you need. Thanks for sharing.