Why am I tired all the time?

i am 15 years old and i noticed that im tired all the time. At night i sleep 6 hours , i wake up , go to school , take my energy pills , go home, eat healthy lunch, take a 3 hours to 5 hours nap , wake up for 3 to 4 hours then i sleep again and it goes on.
on the weekend i sleep almost 12 hours at night if not more. is this normal?
Why am I tired all the time?
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