hey... i completely understand, i am just the same!!
just keep telling yourself that you are not going to be sick, i feel that way every single day, even when i haven't eaten alot! and you definately are not going to be sick. if i feel nauscious, i try and eat something healthy.. it works. and if you are ill, then you are pale and have a white-ish toungue.. that always re-assures me.
good luck 
georgie x
*Hold on to what you love, live for what you know, take everything you dream of, and never let it go*