Extreme fear of throwing up

I've had panic attacks before, and I have had generalized anxiety disorder, social anxiety disorder, and OCD for about a year.
Recently, everything is getting worse. I am 16 and every day at school is so hard. I feel like I am going to throw up from the moment I get on the bus to the moment I get off at my bus stop. It is especially bad on the bus and in the hallways, because it is really crowded and noisy and there is no way for me to throw up/escape from a panic attack without embarrassing myself. My thoughts go from "OMG IM ABOUT TO THROW UP" to "Relax, I'm fine, relax" and back and forth and back and forth. Of course I never have actually thrown up but each day it seems so real.
I don't understand why I am constantly afraid of throwing up and embarrassing myself. I have a really strong stomach; I've only thrown up twice in my lifetime, so it doesn't make sense. And I don't really care what people think. When I am with close friends, family, I am the most outgoing person ever, and when I was younger, I was extremely confident and happy all the time. Now it seems like if one person judges me the world is over.
So my question is, why is it always about throwing up? From what I've read it seems like I'm one of few people who experience this. I have all the other symptoms of anxiety too. Please help, I just want to be able to live.
-Bella