I read this book many years ago, but I can't remember the title or author. It starts with a boy/young man, the protagonist, who undergoes routine surgery, but the surgeons discover advanced electronics inside his stomach. So, he's some kind of disguised robot or cyborg; the protagonist was unaware of that.
He wakes up during the discovery, gets paranoid, and escapes. He quickly becomes a fugitive after the doctors contact some government agency that wants to hunt him down and figure out what he is, going so far as to frame him for killing one of the hospital staff (who was still alive when the protagonist left and before the agents turned up at the hospital). In the end, the protagonist flees somewhere else with a woman he barely knew before that night.
The book has a really downer ending, with no answers provided to what the protagonist really is. The protagonist might have been named Robert, but I'm not entirely sure. As a whole, the book focuses as much on the philosophical questions about the protagonist's artificial nature as to the fugitive plot.