Have you asked him what he does not like about the writing? My son has been an unrealistic over thinker at times. He had issues with writing because he couldn't make his letter look exactly liked typed letters. Maybe you could get some cool grippies for his pencils and tell him these will feel good on his fingers. Sometimes a little change can help. Hope this gets better soon.
Pencil sharpening has been a major issue too. Mechanical pencils have been very important stress relief. This sounds so silly but it's true.
