does your school have a counsellor? that would be the best place to start in finding what might be available in your area.
Counsellors are required to keep things confidential unless of course you or someone else is at risk of harm.
You don't need to have a reason to become depressed - it is a biochemical problem that can really be helped with anti-depressants but being at school can be very stressful.
Many local doctors (GPs, PCPs depending which country you're in) are also happy to manage depression in the beginning and starting meds and if that helps you might not need to see a psychiatrist.
I totally understand not wanting to tell your parents - i'm the same.
Are you able to go to your local dr without your parents? i'm not sure how it works in your country but if they need to know because of insurance or payments you could just tell them you want to go for headaches or some other thing. You've had this for long enough and there is no need to suffer as their are effective treatments.

Good Luck