I don't have double vision and the optometrists/ophthamalogists have never suggested a prism component in my prescriptions. So I don't think that would help. I did have double vision when I was a kid; when I would look towards the sides, one eye would pull in the wrong direction. I had eye muscle surgery back then which corrected that.

I've read that most people's vision gets worse later in the day like you, when their eyes get more tired. But my vision is usually worst in the morning, and somewhat better later on. But even that varies sometimes.