Metabolism and growth make all the difference, Extra. Right now, your body is doing double duty, you're still growing, plus you're working out hard. When you stop growing your metabolism drops down substantially you go to sleep. Many people find that eating heavy before bed causes them to metabolize the food differently.
Eating a heavy meal like steak just before bed (at least when you're out of your 20s) generally interferes with most people's sleep, giving them heartburn, reflux, bad dreams, etc., if nothing else.
I can't even work out that late and go to sleep at a normal hour. If I'm working out after 8:00 p.m. I won't fall asleep until 2:00 a.m.
My son didn't understand it when he was your age, either. He's 10 years older than you and has been noticing the changes in his metabolism over the past few years.