I've just learnt a new word: cacography. It means poor spelling and or handwriting.
This is not a common word (I'd certainly never seen it before) but what a useful word it could be if we revived it:
"I'm not dyslexic, I'm just cacographic."
"The doctor who wrote the prescription obviously suffered from cacography."
"Spelling lessons for cacographers."
Caco- means bad or poor and comes from the Greek, kakos . -graphy is related to writing or recording.