AnonymousI fully understand this. I was similar and had suffered the same sort of thing for a long time - and things were particularly difficult for me as my brother (who is 2 years older) has always been "living life to the full" and has acheived a phenomenal level of success: incredible results in every exam he sat in school, a place in a top university, massive curricular and extra-curricular success there... It seemed that as nothing I could do was ever as good as what he had managed to do when he had been my age, there was no point making an effort. My parents have always been very supportive and quite aware of how completely different our characters are, but that mattered little to me: I was basically as you seem to be to me: not really depressed, simply unmotivated, disinterested and bored. This was compounded by my university offers - five rejections despite excellent grades at AS (AAAAB), and the only offer was much lower than my predicted grades and I wasn't too keen on going there: clearly it seemed to me that the world didn't appreciate my efforts when I did try, so what was the point?
In the end, I was able to break the cycle in a number of ways. Firstly, a good friend of mine fell seriously ill, meaning that she is completely unable to live a normal life. Seeing her miss the second year of sixth form, unable to take her A-levels, and worst of all, compelled to watch all her friends move on to the most exciting period of their lives without her. This made me realise how lucky I actually was! Secondly, an accident causing thousands of pounds worth of damage (covered by insurance but that's besides the point) at our home meant we had to move out for several months; that made me realise how fragile my existence really was, and gave me a new perspective on how little value mere posessions have in the face of memory and experience. Finally, and I hope you don't have to learn this way, my A-level results came out: my results, while good, were far lower than my predicted grades: ABBB, and low Bs in which I had several Ds and even Es in modules. This showed me how little I had worked, and was a real wake-up call as far as work was concerned. I began to take a new perspective on life, and am now thoroughly looking forward to going to university (at the place where I received the low offer, of which I was originally sceptical), where I intend to work hard and live my life to the full!
Of course, none of these things were voluntary: if you want to break the cycle yourself, try some of these.
1. Take part in some kind of regular activity outside school. If this is physical, it could be also good from the point of view of the weight loss. The regular activity will increase your self-discipline and help keep you focused. This could be anything, either functional (I now find myself doing lots of ironing at home! Boring as hell, but someone has to do it) or more for enjoyment.
2. Don't become a recluse - go out with your friends and socialise. Staying in will only mean that you dwell on your negative feelings and this will not help; you need to Do rather than Think, as you have pointed out yourself. Your relationships with others will help define your own character: my relationship with my sick friend gave me real motivation to make something useful with my life.
3. I found that I was wasting a large part of my time playing computer games. This is all well and good in moderation but if you find it prevents you from doing more beneficial things it is easier to kick the habit altogether than to cut down. I sold all my games on eBay and made a tidy sum of cash for university! If you find there is something you do that means you avoid doing more useful things, try and stop: you mentioned your Mp3: try limiting yourself to only using it while out-of-doors or something.
All this may look fairly unrelated, but you may find they help greatly with your personal motivation. Some people thrive on routine; I personally don't, but whether you do the same thing regularly or do lots of random things doesn't really matter, so long as you do things that inspire and interest you. The more varied your activities are, the better.
(sorry if this post makes little sense. I'm trying to help, really!)