Hi . the very fact that you wrote this and want to improve is a good sign.
THIS IS NOT A DISEASE
you need some councilling by a good psychologist
, to build up self confidence and family support.
By becoming more conscious of your daily activities, self motivation and more and more efforts to study you will do well.
Please try to avoid any distractions. like video games,music, internet browsing,too many friends.etc.
Have a goal in life and work towards it.