I really agree with the eating well (just some fresh fruit will go a long way if your diet is as bad as you make out and lots of water) and the sport idea. I know many people have suggested it and you find it difficult with your shifts. But to be honest you have to make the effort if you want to learn more/better. The shift excuse doesn't quite wash with me either, my father is a policeman and he used to run everyday when on shifts, even on night shifts. He still does run although he now only does day shifts. Even just a little bit of exercise at first e.g. 15min run will help. Though admittedly it takes a lot of effort to get yourself out the first few times. I always find after I get up is the best time to go, I'm so knackered after work, and need food etc that nothing will manage to get me out then! Just try it for a couple of months while the weather is good and you'll see :)