Is this stress or something else?

Im 17 and I have exams coming fairly soon. Lately I have found that I have had to walk out of classrooms or leave school as I suddenly start to feel nauseous, get stomach ache and feverish. But it is weird because I won't actually be sick. I found that the stomach ache may possibly be due to changing diet (Im now eating more whole foods as I didn't used to) but I get chest pains and this very odd gurgly feeling in my stomach and I can also get heartburn aswell. Last year I also got a very tight feeling in my chest and I found it very hard to breathe as it felt as if I hadn't fully completed one breath (I had to yawn to breathe) and it seems to have come back again. I also got a very odd clicking sound in my chest when I took a deep breath and this has also come back again. I was wondering does this sound like stress? I get these symptoms very on and off and not all the time. If so, how would I treat it? Since I have exams coming up very soon I don't really want to feel like this!