What is wrong with me? I always feel tired and sick?!

Hi,First off- pregnancy is not a possibility. Im 17 and for the past like 3 weeks i have felt constantly EXHAUSTED. To the point where i keep wanting to stay home and sleep instead of going out with friends. I used to stay up until like 1 in the morning every night and be fine, but now its a struggle to stay up till 830 and i feel tired and weak all day. Just to stay standing in the shower makes me feel a little bit like im gonna pass out. Ive also had an on and off feeling of having a fever/ being dizzy. Any clue what could be going on? I dont even feel myself anymore. All i do is sleep, and wish i was asleep because i feel tired and sick=(