>>7939 (OP)
>struggling to stay awake past 11 pm on any given day
That can be normal depending on how loaded your days are and what hour you wake up.
At around that age I'd also start dozing off between 10 and 11 in the evening and it just doesn't happen anymore because most days are filled with just sitting in front of pc and expending little energy.
>go to bed at 3 am and then wake up two hours later for school
Goes without saying this is unhealthy. But, when you get a few good long naps in a row you accumulate sleep credit that you can later spend on pulling an all-nighter or a few.
You're likely capable of repeating these "feats" if circumstances change a bit.
Visiting a doctor for a checkup wouldn't hurt, sure, but it's probably just the environment and schedule. Maybe you move around more. Maybe you use your brain more. Maybe you diet has gotten worse. Could be a ton of factors.
Until you are an unc, age plays little role, you are too young to have compounded the kind of wear that would turn you into a slug, yet. Still, don't forego getting some good sleep, being constantly deprived can cause bags under eyes, early balding, skin issues, slowed reaction time etc.