My sleep help?????????

Hello,

I am am 17 years old. For the past few months, I have constantly been extremely tiered and practically sleep 70% of the day. I sleep for about 7 hours at night from about 11.30/12 until I have to get up for school ( 7am), but I am always late for school because I cannot hear my alarm clock and am roughly an hour late for school when I do over sleep. I sleep in my lessons and cant focus. I fall asleep on the bus from school and fall asleep when I get home from school. I wake up for about a couple of hours and fall asleep again until i ave to get up for school. This limits me from doing work and I am falling behind in school. Is there any reason to why I am always sooooo tiered and sleepy despite always sleeping. I mean I sometimes would even switch off and and cant control my eyes closing when with someone. What is my problem? And how can I resolve it? I have tried everything to, caffeine, or trying to stay awake for long and I try to keep my selof busy yet none of this works! :(