Tom,
What you describe may be representative of a learning disorder if it has been present from the time in which you first started school. Sometimes those people who have a brain injury (stroke, head injury) or dementia can have similar problems that occur after one has already acquired the ability to express themselves in writing. There are stategies that can be learned to improve this problem in many of these cases. It may be helpful to have neuropsychiatric testing if the reason for this problem is not clear. Good luck.
Sincerely,
HFHS MD-JM
Keywords: Dysgraphia, learning disorder
I am not even close to an expert on any of this, but you might look into Dyslexia, a learning disability.