Hi I had glandular fever during my 4th year standard grade exams and I didn't sit any of them at the time I was supposed to. As long as your have been diagnosed with it and you can get a letter from the hospital or GP, everything will be fine. My school knew for a few days before that I was ill but thought maybe it was just tonsillitis. When I got my blood work back confirming it was glandular fever, my mum called up the school and explained and then the school contacted the doctor to confirm and then they got a letter sent out to the school and I sat my exams a month or so later.
I wouldn't sit the exam if I were you. One because you are ill and not in the right mind set so you probably wouldn't do as well. Two you need bed rest and three I don't think the college would allow you to come in because glandular fever is contagious.
Discuss this over the phone with your college tomorrow. You may be able to do what I done and take the exams a month later with a rep from the exam board in the room with you or yes you may have to redo the year but I highly doubt that.