Hi schoolboy, Welcome to Healing Well forum. There are lots of kind caring people here always willing to help each other. Also this site can be a never ending supply of information for anything that you are going through or question from mental to medical.
In your post you didn't mention anything of feeling depressed or having a past history of depression. So I would wonder if this is really the cause of the problem that you are having. It could be caused by stress but I would be more likely to think that you may have a touch of Attention Deficit Disorder or something more along these lines. Have you ever been checked for this? Or you could have a medical problem going on. Maybe check with your family doctor and speak to him about it and see what he says.
I also have had the same problem all through my life. I am 32 now and working on my masters in psychology. In school I always just thought that I was not a smart as everyone else as I had to work harder to remember everything and study more. It was very stressful for me. Anyway, I was diagnosed with Multiple Sclerosis in 2001. This disease fatigues you to no end. I was put on Ritalin to combat the fatigue and since my memory recall has improved greatly. My attention span I am able to focus on what I am doing instead of everything else. I have not been tested or diagnosed with ADD. So I don't know if my problem is because of ADD or MS, I just wanted to note.