Wish you both the best of luck for your midyears, Stick and Surgeon! Hopefully any issues will have a minimal impact on your results.

With the sore hand thing - that used to happen to me all the time (I was obsessed with drawing, lol). I've found that sticking your hand into cold water (or applying an icepack or something), holding it there for a few seconds, and then repeating the process with hot water helps to relax the muscles a bit. Tried it out after eavesdropping on a convo someone had with a P.E. teacher about hot-cold showers...

You can also try creams to numb muscle pain, which would be much more convenient for SACs/exams.
Aside from that, you can try switching pens to thinner/thicker ones at regular intervals, so your hand isn't always in the exact same position. If you find you tend to grip the pen too hard, try getting those squishy grip things. Never used them, but they might help.
Just going to throw in some pen suggestions as well, while I'm at it.

Writing is so much easier when you have a good pen! I've found that
these and the black/blue version of
these are quite easy to write with, since there isn't much drag on the page, but it's all down to personal preference.
But ultimately, you need to rest! I know that studying is important, but your health is much more so. If you really, really feel as though you still want to study, then read your notes; there's no point doing heaps of work, only to be unable to write properly in the SAC/exam.