To answer your question simply, yes, you can miscarry without knowing it, or having any symptoms of miscarriage...as others have said, it is called a "missed miscarriage" or a "silent miscarriage." I had one back in July of 2011...I was 11 weeks along, when I discovered at a scan that the baby did not develop beyond 6 weeks or so.
Since you're really early, I wouldn't worry. Symptoms can be sporadic at this point, or even nonexistent. You may just not feel terribly pregnant yet, and that's completely normal.