Sleep and diet by far.
I use to feel like you a lot, especially after coming home from school and im involved in 4 different sport clubs and i could barely be botherd to do any sport during the week.
The best thing which works for me is sleep, you might not think so but honestly you really do notice it, maybe not so much during the morning and lunch time but your notice it especially around late afternoon time you dont feel as exhausted or anything, well i really noticed the difference after sleeping for 10 hours than say 5 or 6 hours.
Also try eating a good balanced diet, especially breakfast and drink lots of water, if your looking for a specific drink then i drink a lot of lucozade in the mornings for lunch and before playing sport, not the fizzy stuff but the orange juice type ones, much better than the vial red bull.