Why am I so tired all the time?

i always feel exhausted. I am a freshman in college and I try to go to bed around 11:30, but lately, I have not been able to fall asleep until around one. I just lay there and can't fall asleep. but then I get up for class at 8 and I basically sleep/space out during my class. once class is over, I go back to my room and sleep until about lunch time. but even then I sometimes sleep through lunch because I am so tired. I am starting to wonder if I have mono or something, but I don't really have any other symptoms of being sick. any ideas of what might be wrong?
Why am I so tired all the time?
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