Hello Zara, please let me welcome you to the site and I'm truly sorry for how you are feeling and there doesn't have to be any particular reason why you are the way you are feeling, because mental illness is different than having a broken leg, that's something people can see, but not with how you are feeling.
Can I suggest that you click on 'The Facts' and scroll down until you see 'K-10', it's a depression test and try to do it several times, but not straight after the other, but different times of the day and keep these results.
Then can you write down how you feel, that is, what you can do or what you actually do during the day and what stops you from being able to do, and just add to this list whatever you feel.
Book an appointment with your doctor and then show them the list as well as the K-10 results, then they will make diagnose you and then refer you to a psychologist if needed.
Ask them about the 'mental health plan', this entitles you to 10 Medicare paid sessions per year to see a psychologist who you feel comfortable with.
You can also contact Kids Helpline who talk to people up to the age of 25 on 1800 55 1800.
Please don't be afraid, we are here to help you along this journey and hope you can get back to us.