I also used to read a lot of fanfiction and I still do sometimes. Fanfictions sometimes helped me finding new books. Maybe try to read one about characters of a book or a fanfiction with characters that like reading. That might motivate you into reading new books. And if you think you read too much fanfiction maybe consider imposing some sort of limit. Like two books a fanfiction or use fanfictions as a small reward for a new achievement.