Why can't i work

Work has never been my strong point, I have always struggled with keeping my mind focussed on one particular thing for longer than that of a rather intellectual goldfish.
I'm not quite sure why this is, maybe it's too much caffeine, not enough exercise, too much greasy food, too much television, too many computer games......whatever it is i'm sure i've had too much of it! (except exercise of course)
I've never been much of a positive thinker, it's something I struggle with, it always seems so much easier to look at negatives. Whilst on the phone to mum on the way home complaining about how 'I can't do this, I can't do that', mum pointed out something ver profound to me - 'I've not heard you say a positive thing about you and your work so far.' - I think she was onto something there.
Lets be honest, I have done a lot of revision (for me), but all I see is the massive mountain ahead of me, not the half mountain that I've already conquered. She reminded me that it is important to remember the positives, PMA and all that jazz. From now on I'm going to do my best to try and be positive about what I've already done, and even more positive that I can carry on and not let the dreaded exams beat me.