Yeah I have the same problem and my teachers have just given up on telling me. Its obviously not something you can change easily, but my teacher made me aware of the fact that it just means that everything I say needs to be effective and waffle-less- well as it should be anyway. But more so for messy handwriting, which makes sense. What the examiners read, out of shit shit they cant read, needs to be effective.
And I find my handwritting deteriorates further along an exam. At the start its neat, but towards the end it gets more illegible because I slack off and I just cant wait till its over.
I think, for english, I'm lucky that I do Language Analysis first because my writing would be better then
And I'm thinking of doing context last, in which I should be able to get away with messy handwriting because, the essay is essentially waffle.