Sometimes (okay, many times) men are not all that great at talking about their feelings. Maybe he feels that just not responding is easier than explaining that he needs some space. It sure sounds that way.
When I was much younger, I was way too clingy and wanted to be connected to my guy pretty much all the time. I can't imagine how many guys I drove away by just being too clingy and not giving them any room to breathe.
Again, just stepping back and not contacting him for a few days will let you know if he needs the space and time away from you. After all, he knows how to reach you if he wants to talk to you.