Reading Comprehension?!?!?

Ok, so when I read anything educational, like a textbook from school, or those articles teachers give you along with comprehension questions, I don't understand a thing being said. Like I could read a sentence literally ten times, and still not be able to understand what they're talking about. What's my problem? No I don't have dyslexia, I could read fine. I read fiction books for fun, and I get their plots. Does anyone know what I may have, or what problems I'm dealing with?