If you are not sure that he raped you, he must have washed away the evidence. If you had acted right away by going to the authorities, they could have possibly gotten some DNA evidence. He could also have been recorded as a suspect in another report. So, when records build up, someone will nab him sooner or later because rapists do not usually have the intelligence to stop. He probably use that date rape drug, rhohipnol, or whatever it is called. It is not easily detected in the body according to an article I read a few years ago.
It is not too late to report your story. The majority of victims do not report rape, especially Black women and males of most races. Some victims feel that they won't be believed, and yes, rape is hard to prove in some cases. If you are under 18, you may get more attention. Do not worry about not being able to prove it. Get some support and report it!
I wish you well.