MEGirl, watch those tonsils. My eldest had tonsillitis often as a younger child and had a few minor bouts in year 11. We were always told he'd grow out of it and tonsillectomies weren't done much nowadays.
Two days before AS levels he went down with an appalling bouthe had glands swollen in his abdomen, a very high temperature and was just very, very ill. The GP thought he might have glandular fever. We managed to wrangle a whole 2% 'consideration' on the AS level exams he dragged himself into school to takeGod knows how! He didn't do badly in the papersp, but missed out on the very useful extra UMS points that could have bumped up his results in the harder A2s. He actually missed his university offers by one grade, about three raw marks in one subject and is going somewhere else now. It has all worked out well, but has been very stressful.
We actually paid for him to have the tonsils removed in the October of Year 13 after another very bad episode, because, when we finally got the NHS to agree they needed to come out, they couldn't have fitted him in for eight months, which would have taken us right up to A2s. The surgeon said the tonsils were horrendous when he removed them--covered in scar tissue. The operation cost £4,000 and was a real financial wrench, but we felt we had no option but to pay.
So, if you sense this is becoming a recurrent problem (and it may not be), try and persuade them to take action and take the damn things out. They don't like doing it, for understandable reasons (it's not a pleasant operation and lots of people do grow out of it), but taking important public exams when you feel so ill is awful. And I think the stress did play a part in the really bad episode just before AS levels.