I think I have some kind of psychological disorder?

I'm eighteen, I've gotten through puberty and all that. I'm near positive it's not hormones that's making me like this. I'm extremely temperamental and I have consistent suicidal thoughts, and violent thoughts. I get anxious around too many people, and I start tearing up and getting scared. I'm extremely pessimistic and I have the absolute WORST self esteem. One minute, I can be perfectly fine, and the next I'm balling my eyes out because I feel like I don't belong and I feel worthless and uninteresting. I was so hard on myself when I went to my college orientation because everyone there was super shy and getting to know each other, and I literally felt like I didn't deserve to talk to anybody because everyone was 10x more attractive than me, and 10x more interesting. And when I did have conversations with people, I stopped talking after a minute or two because I felt like nothing I could say would be interesting. I can't look in mirrors because I start crying. I feel like everyone's making fun of me all the time. I come off as super nice but extremely soft-spoken to people, and I feel like everyone thinks I'm weird and nobody likes me. I'm an art student/major, and I have zero inspiration to do anything because I'm so scattered and unorganized and I'm repetitive. I'm scared to go to school because I feel like I won't make any friends, even when I try to be friendly. And I'm scared I won't do well in my art classes because I can't stop repeating myself. I have panic attacks almost every single day, and I cry myself to sleep. I have a younger brother, and I used to shrug it off when he was mean to me, but as I started to get older I couldn't handle it anymore. And he makes me want to kill myself. And I try to be happy and I try to find things to do that take my mind off of unpleasant thoughts but it doesn't seem to last very long at all, and I feel like there's nothing I can do about it.