You should definitely talk to your teachers/ the people coordinating the exams. Nystagmus can be a pain when reading and if you’re tired, the exam isn’t testing your knowledge, it’s testing your vision. I’ve messed up quite a few tests (especially math and bio) because of my nystagmus. I also have to retake a course because despite me trying to get the stuff in advance I didn’t have the accommodations I needed which meant I was anxious and my nystagmus rendered my eyes useless. While it sucks, you should remind you’re school about the stuff you need early and often so that you don’t end up in a situation like mine. Another thing that help is seeing if you can get audio of the text in case your eyes aren’t cooperating. I also find that A4 size paper works best for me as it means there’s less places to get lost due to nystagmus. I wish you luck in sorting this out! :)

Ps. If your eyes are acting up during the exam, let your teacher know.

Ask your school if any of your exams can be postponed to the next day on the condition that you don't discuss the content with others. Sitting four 1.25-hour exams in one day sounds like it will be too much, especially as you have said that reading large print makes you tired.