feeling completely crushed

Amy
My boss is actively trying to fire me bc she doesn't like the way I work. I have never had this happen with ANY other position I've held and have always been a bit of an overachiever at work... so it's just thrown me for a complete loop that she thinks I'm doing such a horrible job. I literally have no idea what I can possibly do to improve Bc I'm doing EVERYTHING she asks me to in the way she is asking me to do it... and when I ask for pointers she gives me a dirty look and says she's already told me what to do to fix it.  
Then she asks what she can help with so I will ask for 1-2 things that are pretty minor for her but would be huge for me... and she gives me another dirty look and says that those things are my job... 
I took about 5 steps backwards career wise for this position bc I wanted to get into the company and was willing to work my way back up... I just have NO FUCKING CLUE what I can do to make this work.  
It's to the point where I literally have been crying on and off for like 18 hours- I feel sick and can barely keep water down. 
I'm in full fight or flight mode and I just want to kick her in the throat and quit.