Gotten ill a month before exams!Watch
Go to the doctors as soon as possible. Hopefully it'll be easily sorted, but in case it was something slightly more serious, they would give you a diagnosis, and this can be explained in advance to the exam board, who can (in exceptional circumstances) make exceptions. Just eat your chicken soup and look after yourself.
Also, it may sound silly, but try not to sleep too much! Sleep 8 hours a day, and have an alarm in the morning to wake you up after that duration. Too much sleep can make you much more tired and more ill. (I have chronic fatigue syndrome, trust me!)
It won't ruin your chances! Do as much revision as you can in the times during the day where you're feelign "most" awake and do your best. I got 4 A*s and 5 As in the end! Which was okayy, I would have done better had I not been ill, but it's still good! Good luck