Getting distracted or sleepy while reading?

For a lot of my life, I didn't read. It's a recent interest of mine (4 years or so now) and I've always struggled with staying focused and awake while reading. I'll carve out some time where I have 3 hours or so I'd like to read for and after 20 minutes I've lost focus and realize I have to flip back several pages to re read things.

What tips do you have to retain your reading and focus better? Audio books have helped a lot. I can listen to them for hours and not miss a beat, but when I open a book I seem to lose it.