It's just nerves, possibly brought on by an anxiety disorder. As someone who suffers from social phobia and an anxiety disorder, all i can suggest is that (depending on how greatly you feel this impacts your life, like causing you to avoid events or confrontations) you speak to a therapist. I worked with a process called Cognitive Behavioural Therapy, which is the most common form of therapy for this sort of thing, for over a year. You can look up information about it but the long and short of it is that you consider the situation that causes you stress / anxiety, consider your immediate thoughts and reactions to it, then list the evidence for and against those thoughts, and then end with a more balanced thought.
It may not be an anxiety disorder you have, but rather, just nerves. I used to be the same when i was younger. For example, the first time people disagreed with me harshly on a forum or i got quoted when i knew i said something controversial made me get that same queasy feeling you get when you're about to look at your exam results for the first time, but that went with time. I'd say just ride it out. If it doesn't go away after a few months of being here and interacting with people more, go and see a therapist.