Hi, this has happened to me ever since I can remember. Concentrating on something important - like exams, school, doctor's appointments - seems almost impossible for me. The only haven I found was in music, or drawing. If I'm not doing either of those things, I can't concentrate on anything else. Now I keep my earphones and I-pod with me where ever I go, and a sketchpad in my bag just in case.
When I told this to my psychiatrist, he told me to write down these thoughts and label the date, so I can come back to it later and see what has been keeping me occupied. With some issues, once I figured out what the notes meant, I stopped thinking about that subject all together, but on others they keep repeating.