What's wrong with me? I'm losing it!?

I'm a 16 year old girl. I live a happy life, but my family has a history of severe panic and anxiety/depression problems. I'm also struggling with bulimia. I'm 5'4 119 pounds and generally very healthy. I can run a mile in 7:30 minutes. A few days ago I started getting shortness of breath. My chest hurt a little bit and also my arms and legs began to hurt especially in my joints. I wake up extremely early as well. I went to the doctor because I thought I was having a heart attack. She said I was fine and that it was anxiety related. It's been 3 days and I feel the same. I still feel like I'm going to die. I spend all of my time feeling paranoid and like my life is going to end any moment. I think everything I do is going to be the last thing I do. I worry constantly about the people I care about too. If someone doesn't answer their phone I lose it and think they're dead or have been in a horrible accident. I can't stand to walk alone anymore either. I feel like someone is going to jump out and rape me or kill me. I have also developed an intense fear of my bedroom and can't sleep in it. I feel like I'm on the verge of a breakdown and I don't know what to do. I worry so much that I feel like I'm going to explode. I'm so tired of being terrified of death and assuming that it's right around the corner. I don't know what to do. I feel like i need to be admitted in a psychiatric facility. Help me :(