I know just how you feel, and I also know how stressful it is going into an exam when you know you haven't revised enough!
I struggled with this all through secondary school and college. I was given the benefit of the doubt several times, and allowed second chances (such as resitting the whole AS Chemistry course), but it hasn't seemed to have eased with time. The whole thing is detrimental to my education. I always tell myself that I'll start revision earlier, but it's like there's a physical barrier. I've just finished my foundation year at University and I need to revise for a couple of exams...
The only things I can suggest, if you haven't done so already, are:
- Logout of facebook/twitter/any other social media
- Check out the 'focus' playlists on Spotify. Some of these are pretty useful
- Declutter your work space. Don't leave things around that'll distract you. Then again, don't use this cleaning up as a way to procrastinate (something I end up doing)
- Get enough sleep every night. It's even harder to focus when you're sleep deprived
- Don't overdo it on the caffeine. This tends to make me into a ball of energy and then I want to do anything besides study
- Make a revision plan. If you can't bring yourself to do this, at least aim to do a certain amount of work before having a break (and I don't mean a week-long break)! I use this app called 'Forest'. This has actually helped quite a bit. You have a tree to grow and if you close the app, the tree dies
- Attend revision sessions at school, or work in the library. It's usually easier to revise when there's teachers around and limited distractions
- Eat well and exercise. Sounds like I'm just preaching, but both can boost good neurotransmitters (like serotonin) and give you an energy boost too.
I'm trying to think of more, and I'll post them here if possible. Oh yeah, one thing that helped me last time I had an assignment due was writing a note to myself. In it, I just bullet-pointed the reasons I NEED to get the work done. I put this by my PC screen so I saw it often.
If none of this helps, I seriously suggest taking a trip to the docs and enquiring aboit ADHD. I wish I had done sooner, and right now I'm too anxious to even go to the GP.