A less well - known but great option is 'All Our Wrong Todays' by Elan Mastai. The story has a unique take on time travel in a science - fiction context. The main character is dealing with his own issues and making sense of his life, much like the characters in 'The Fault in Our Stars' are dealing with their own situations. It has a bit of a philosophical undertone as well as the science - fiction aspects that make it an interesting read.
Well, 'Ready Player One' by Ernest Cline is somewhat similar. It has a young protagonist who is on an adventure in a virtual world filled with science - fiction elements. While it doesn't have the same illness - centered plot as 'The Fault in Our Stars', it has that sense of a young person dealing with the world around them in a unique and challenging setting.