I don't have ADHD -
I can't read a book all the way through because I'm just that way...too hyper, too distracted and not interested
I day dream because I'm bored so sometimes my mind wonders
I read stuff over and over again and usually it's because I'm stressed or rushing and I need to go back to see it or I have to say it out loud in front of someone before I actually get it
Like I said, I think you don't have it because it would be very hard (not just "not being able to pay attention sometimes").
Anyways, my advice is to go to a GP or your doctor at a clinic. He can refer you to a psychiatrist if he sees it fit