First of all, don't panic! There are plenty of people who probably woke up today feeling ill before an exam. Unfortunately, in most circumstances, you will just have to put up with it and just try your best. If it's extremely bad and you physically can't take the exam then you will need to go to your GP and ask for a note explaining that your performance will be affected by your illness. In this case, if you give the note to an invigilator, you might be able to achieve a 3-5% increase in your mark. However, I'm not entirely sure that this % increase is valid for minor illness. Usually, they're for people who have had surgery or a relative has died, for example.
The best thing to do is to take cough sweets, Lemsip, vitamin C (Berocca for instance) and gargle salt water (very effective, gets rid of sore throats almost instantly). Keep focused and try to ignore your throat. If you've put the work in already then I'm sure you'll do brilliantly (I also have these exams tomorrow so I'll feel your pain xP)
Wish you the best luck for tomorrow!