I don't like to do anything at school

I used to get good grades in elementary school, A's and B's, but since 8th and 9th grade I just don't want to work or do anything, I do my homework but I always forget to turn it in and the teachers never ask for it you gotta turn it on your own time and all I do is play on my phone, listen to music, sleep, talk with friends, sometimes do work and I'm not sure what's wrong really.