I'm sorry you're in this situation. When I was in high school my parents were not supportive of me either, they got angry at me instead of helping me.
I never saw a therapist until I was on my own in college at 18, then I started seeing a therapist. Better late than never right? Because it's at my college it's affordable for me to pay on my own.
But I think it would be best for you (and for everyone in general) to get help as soon as possible, so do you think you could tell them kind of what you told us here? You could play it down a bit, like maybe you're "just feeling a little down" and you want to see a therapist to clear things up, so that you are a great candidate to be an FBI agent.
I wish you luck, I know situations with parents can be hard. Keep us updated.