Absent Minded in school/home?

My parents and teachers say i keep forgetting alot of things, being absent-minded, spaceing out to… I had A’s and B’s the year before, Now its Mostly, C’s and D’s, im doing worse now, and I don’t know why, teachers say im not focusing, or concentrating. They say i try, but isn’t able to, i really want to get my grades up. Could it be because of this game i started playing..? im really addicted to it. i also do all of my homework and do pretty good on them, and i also study for my tests/ quizs, but i fail them, and thats how my grades go down.. And also, my teachers tell me to do something and i don’t do it, they say its because im spaceing out. Basicly, what im trying to say is, how do i stop spaceing out/ being absent-minded?