Mood Swings??

So I've been having mood swings for the past three days. Everything has been annoying me, and makes me real irritable. I've been sensitive and confrontation lately and this is unlike me. I NEVER get this irritable until about two days before my period. My period isn't due for another 3 weeks. I have no reason to be upset, so why am I so upset like my period is about to start? I have been feeling a little nausea as well, but just mild, and only lasts for about 5-10 mins every day. Could I be pregnant? If I am then I can only be about a week for sure...