I can't read non-fiction...?

Part of your problem may be as to whether or not you are actually interested in the subject of the non-fiction. Often times if you are simply reading the book because it was assigned to you, you really do not have a personal interest in it. When you don't have a person interest in the subject, it's hard to retain the information because subconsciously you do not want the information.

However, you could try taking notes as you read. Or after every chapter/section try talking about it. Even if you are simply talking to yourself. Talk about what you read, what you find remotely interesting, discover the timeline, etc.

I can't either and don't force yourself to I hate nonfiction