How can I abstain from using the internet when I have better things to do?

I realize how my addiction to the internet is ruining both my character and my intellect. It seems like every time I sit down and try to study or read a book, my mind inadvertently wonders whether communitychannel has been making any new videos lately, or if I have any new notifications on facebook or something. All this is so stupid, and has really hurt my school grades. Last year I barely touched the computer, and I did all my homework on time and actually could focus in my studies. I was smart then. My mind was sharp. But this year ( 9th grade, the year things start to matter), I wasted all of the three days before my final exams fooling around on facebook. So I had to cram about 10 chapters of math the night before. OMG, right? I still somehow managed to get an ok score, but I knew I could've done was better. Also, my obsession has also taken a toll on my emotional well-being. For some reason, going on facebook and youtube makes me feel depressed and agitated. Reading has always helped me let go of stress, but now I'm never even in the mood to pick up a book! About 2 hours ago, I'd promised myself I would finish the first draft of a short story I plannned on writing. But after 10 minutes, I find myself here. On the stupid, evil, and seductive INTERNET! GOD. I really need help getting out of this now. What can I do? :(