Gotta add, I have to agree with the people who said go as soon as you can, I'd say go tomorrow after the exam, since it's probably too late now to go today
My ex had apendicitis recently (Not that she realised it was that at the time) She didn't really prioritise going to the doctors over anything else and ended up rushed to hospital and stayed there for 2 weeks.
I understand you don't wanna miss an important exam, but I'd much rather be in safe hands than risk it for education.
Are there no resits or anything? Exam boards should sympathise with you if you explained to them the situation, I'm pretty sure of it.