This is somewhat of a common problem unfortunately, but there are ways to remediate that and stay focused. My best piece of advice would be to create a plan and write it down. Set yourself timeline goals, check it daily and complete the tasks you have set out for yourself. Usually people who get distracted are visual learners and having something tangible to see, read and manipulate can help keep you on task.
I would agree with the person before. If this becomes a chronic problem, I would speak with a medical professional about help focusing. Regarding your career, I would suggest speaking with your school guidance counselor or taking a career aptitude test to decide what professions may be right for you based on your strengths and passions.