It could have something to do with ADD/ADHD, but I think it's more likely you're just having trouble getting interested in the book itself. When I was younger I'd read almost every night before bed. I have ADD, and I would use a book as a tool to help me fall asleep. It took me a few years to realize this. At night right before bed, I'm not usually able to just lay my head down on the pillow and conk out, because my mind would bounce from this or that, and having my mind focus on one thing for an hour or two would help my mind focus on one thing, and finally gear down and relax enough for me to fall asleep.
This is also why I probably wear glasses today. As a littlun I had a bed time at 9 pm. I couldn't just conk out right away at 2100 because my mind was just as hyper at night as my body was during the day. So I'd read goosebumps (revenge of the garden gnomes was one I must have read over a dozen times) by nightlight for a few hours 'till I could fall asleep. Basically the equivalent of reading by candle light, the strain of focusing on small print in low light over time fucks with your eyesight.