Growth could be a factor, but what are you eating? Are you eating good, healthy, filling foods that will sustain you through your day? If you're like a lot of teens, a lot of what you eat may be junk and empty calories. As an athlete, that may not sustain you. It could also be affecting your blood sugar, with spikes and crashes.
The back and knee pain should be checked by a doctor, though, especially since you're an athlete and active. While you're there, talk to them about your hunger and fatigue. They may want to rule out some things, especially if you're eating well.
Let us know what happens.
I'd check with a doctor to see if there are any metabolic/thyroid issues going on. Low back pain and fatigue can each have a lot of different causes and could be related or unrelated, but should be checked out as well. How's your overall energy level in between? Do you feel full after eating, but then get hungry more quickly, or need to eat more to feel full, or never feel full?
Could be Kidney Failure .