Help me please, Am I crazy?!

I think I am going crazy. This had been going on for awhile now.
I don't know who I am, like sometimes I would think to myself, "Why was I born?" or "Why am I living in this body?!" I ask myself all of these questions that just build up inside of me. Sometimes I feel like I'm not supposed to be living in this time period, I am more into old fashion, vintage things or maybe the 80's but not in this time period. I honestly hate it.
I think of the past and future alot, I think about the different ways of living life and what I could of done to make it better. I even think about my death, how I want to donate my body to a laboratory when I die or how it'll feel to be burried 8ft underground inside a lonely box. I think of what would happen to me after I die, will I feel like I'm still living when I'm dead?!
I think about why I was chosen to live, I'm Atheist so it's actually very hard for me to believe when people say "God chose you for a reason" or anything related with "God" giving life to me.
Sometimes when I overthink the feeling of death I get so nervous I can't breathe, I feel like I'm going to die any second I can't bare to be alone and I just want to go outside and somehow run to a place where there would be alot of people like a busy city or something so I won't feel like I'll die alone.
All of this makes me feel sad, I don't eat, I lose interest; all because of this. I just want to be alone or rather die. I feel like I'm going crazy. Help?!