Gaviscon and diarrhoea? ?

I've had diarrhoea on and off for the past 5 weeks and we put it down to nerves due to my exams! My bellys been making a really loud rumbling noise and then I have diarrhoea so my dad said to take a gaviscon tablet- (at 10am this morning) I was fine and I felt much better so I ate a couple of rich tea biscuits! Its no 12:35 and my stomach hurts again! What shall I do? I also nearly fainted twice yesterday and I feel dizzy (possibly cause I haven't eaten tidy due to the fact I get diarrhoea after I eat!) What could I have, or is it just nervous making me like this? Please help me? Thank you in advance!:-)