I have too much weakness, excessive drowsiness, loss of appetite ...

I have felt a lot of weakness, excessive drowsiness, loss of appetite. I am tired with little physical effort, I have persistent sadness. Ideas of death and empty feeling. Please, I really need your help. Because I'm just a 17-year-old, and I do not see it in other girls my age. Can you suggest what I would be and a doctor I can go to for an accurate diagnosis? Thank you in advance.