Psychiatric problem. With difficulty!

Poor concentration can be a result of multiple psychological, psychiatric, or medical problems. However most common causes at your age can be poor interest in subject matter, easy distractibility, depression, stress, alcohol use, anemia, thyroid disorders etc. I would recommend that you should get yourself evaluated by a psychiatrist to identity the causes behind poor concentration. However in the meanwhile following steps are likely to benefit you- 1. Take regular diet and have a regular sleep with regular sleeping and waking times 2. Meditation/ yoga/ walking/ jogging etc will help you attain a calm state of mind and will help in concentration 3. Avoid use of alcohol/ tobacco/ excess tea or coffee 4. Identity a calm well lighted space with minimum distraction as place of study 5. Avoid all distractions like TV/mobile etc in study duration 6. Writing notes while studying helps in maintaining focus 7. Revise what you read regularly for higher retention and reproducibility 8. Take 10- 15 min break after 45-50 min of study 9. Do light activities in break duration avoid TV and mobile here also 10. Discuss with your friends regarding study matter or better still form a study group Hope this helps you..