Depression? Suicide?

I'm 21 years old and go about 3-4 years I've been suffering from depression. I never got diagnosed because I'm scared to finally talk about it to someone face to face. I've swallowed half a bottle of extra strenght Advil when I was 18 in an attempt to kill myself. On a daily basis I think about killing myself, turning my car towards oncoming traffic. I used to be so social I used to love going out meeting people but for a few years I've just isolated myself, been sad all the time, I have self loathing. I feel like if anything goes wrong in my life it'll push me off the edge. I've tried talking to my mom once but she just thought it was a puberty, that there are worse things going on in the world than me being sad. I don't know if I'm crazy or if I need help. 

I heard that antidepressants can actually make you sadder and I don't want that. I just no longer want to live, I'm sad and I don't know why.