Greetings of the day.
I went through your query and there may be multiple reasons for the same.
Some of the reasons might be- a deficit in the ability, having conditions like ADHD, poor learning strategies, emotional issues, etc.
Some simple strategies can be doing sorting and cancellation tasks, having proper diet and sleep along with doing some physical exercise.
I would recommend you to meet a clinical psychologist for proper diagnosis and management of the problem, if it persists.