Hello Friend, Good that you are seeking a help here. Anxiety is the reason for such lack of concentration or poor memory. You need to follow certain lifestyle routines change, excersise, self behavioral therapies and dietary changes to overcome anxiety. This is a natural non medicine solution and can help you for long term to manage anxiety. Feel free reach to reach out to me online for further evaluation and recommendation.

An average attention span of an individual is 20-30 mins. After which you are bound to get distracted. Are you able to learn and recall what you have done in those 20 mins? If yes then nothing to worry about. Don't try to study at a stretch. Take small breaks of 10 mins to refresh yourself. Before learning - 1. Preview the content. 2.  Questions yourself what is the content all about. 3. Read the content 4. Recite what you have read. 5. Test your self by writing how much you remember. Keep flipping through the notes of the topics you have studied. We have a tendency to forget what we have learned.