Genera feeling of unease

I was just wondering if anyone could help with this. For the past while now, I've had this terrible feeling. It's hard to describe but it manifests itself physically as this "tightness" in my stomach. I also feel slightly overwhelmed and frightened but I don't know why or what it is that's causing this. I originally thought that it was just Leaving Cert pressure but I now feel that it's something else because I've begun to view the leaving cert as more of an annoyance now. I still feel the pressure but that's only because I'm going for a high points course. I have noticed that I feel worse whenever I think about school. It's really become a them versus me situation with them doing all the socialising and drinking and partying and me staying at home by myself. But it's always been this way, I've always been different and separate from them and I don't see how this could have gotten worse so suddenly.
Does anyone out there have any idea what happened to make me act this way?