if you can't focus on what you need to do, then what are you focusing on? maybe if you can find that out, then you can do something about it,
like, are you getting distracted by wanting to go on the computer or watch tv or talk on the phone?
or maybe you have other problems that depress you so much that your just constantly thinking about it, or you just don't feel like doing anything, even though you know you should,
like my sister is constantly depressed about her weight, she won't work, she won't go out and do anything, she can't talk without getting mad about something, no matter how big or small...

i do have the problems with not being able to keep my mind on one thing, but like the others who posted, i also don't have the answers, so thats all i could come up with :|