How to get myself to do homework and ignments?

Im not sure if I actually ADD, but its self diagnosed :P. I am a very smart guy, ive made it up to grade 12 making honour roll while doing seldom homework and ignments (I know lol, i do very well on tests). Anyways, I realize this can no longer continue. However, I cannot force myself to stay on task with my homework/ignments. I would lock myself in my room and sleep on my homework, unplug my internet and eventually play minesweeper, I try to manually write up ignments and instead doodle, etc. I'm not sure how to force myself to do homework and ignments. Any help?