Hello Friend, Good that you are seeking a help here. Your mind may be pre occupied with thoughts due to stress or anxiety which in turn affects your memory and concentration.
Obviously when your mind is emotionally disturbed, it exhibits physically distress like fatigue, dullness,disturbed sleep, lack of appetite and many more.
So it's better to have a holistic approach to analyze and isolate the root cause and treat it rather treating the symptoms.
Next Steps
Feel free to reach out to me online through Practo for further detailed evaluation and suitable recommendation that you can follow practically to overcome this problem. Solution could be few lifestyle changes, dietary, self therapies or exercise etc. Be confident. You will be alright soon.