Maybe you are having attention deficit disorder. Consult a psychiatrist. Nowadays there are very nice medicines to improve concentration. Check yourself for OCD also.

Hello Dear, Rumination is something which can keep us in a distracted to heavily troubled position on a scale. It's awesome that you realize that mind can be in our control. You also has taken a step towards making it so and have succeeded for a while. You mentioned that the thoughts which have been rising in your head and distracting you are unnecessary ones. We will have to change the perspective a little and listen to them for a while and understand what all they are about. Please listen to them for 15 days and put them under different themes or sections. Keep expanding and understanding each theme. After 15 days, allot a time when you would intentionally think about all these themes, every day. In a month the chatter in your head should clear to an extent. If there arise some thoughts or emotions which confuse or trouble you, consult a psychologist who would help you understand them better and channelize them. Take Care.