Umm wow, there are entire books that seek to answer those questions. Really competitive freedivers keep to incredibly specific diets and since I don't mess around with the sport that seriously, I'll avoid putting my foot in my mouth (pardon the pun). As for me, before a day of spearing I'll avoid heavy foods. The night before I'll eat a light meal and make sure to gets veggies and some carbs (but I don't carb up as if I were going for a long run). The morning of, I avoid coffee and will have a very light breakfeast of yogurt or a granola bar. I usually bring a little food (granola bar) with me for the dive in case I crave something.
Ideally you should dive on an empty stomach, but I've heard from divers that this can make them queezy. I don't really have any problems with the empty stomach making me queezy, but I find that since I'm usually doing several hours of spearing and not necessarily any really long breathholds, having a little food/energy is more important that maximizing my apnea abilities. So I eat a little food, but not enough so that it weighs me down.
Now the after dive meal usually consists of very fresh fish and at least a half dozen beers (diving dehydrates you)
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As for your situation. Don't listen to adults who tell you that it's not good for you to sleep so much. Teens eat and sleep a lot because they are growing a lot. The additional food and additional sleep are absolutely necessary. A teen should sleep 11-13 hours a day, whereas a regular person only sleeps 6-8 with older people more towards the 6 end of that spectrum. So chow down and get your rest.
As for what not to eat and what types of food can make you tired. Any complex carbohydrates are not going to be good foods to eat prior to a dive (since you're body is going to expend energy breaking them down and this can tire you out and slow you down). Simple carbohydrates are best. Simple natural sugars are good too (oranges are excellent to keep around). Artificial sugars are not good. Obviously really fatty foods will also slow you down, so avoid those too.
These suggestions are based on limited knowledge of nutrition and personal experience with exercise and spearfishing. As i said above, competitive freediving is a much more physiologically sensitive sport and a freediving diet will very significant from what a regular spearos diet will consist of, as will their exercise routine.
