Hmm.
Yes, communication isn't a one-way street, but here are a few
things to consider:
1) Communication is not limited to the verbal - just because she's
not saying anything doesn't mean she's not telling you
anything.
2) For some reason or other, she obviously doesn't feel comfortable
telling you what's on her mind. Note, though, that this may not be
any of your doing - she may simply feel that what she says needs an
audience of a different mindset to yours if she's to be
understood.
3) On the other hand, if your normal pattern of communication is
reflected in how you've written your posts here, it's not ideal for
such a situation. Obviously, if she's saying it's "nothing", it's
going to be something that she does not find easy to talk about.
Judging PURELY by the way you've been writing here, there's a lack
of the patience that's required if she's to feel safe enough to
speak her mind.
To illustrate the extent of patience I'm talking about, I'll
present the Seven-Hour Clock. Shortly after my girlfriend and I
started dating (we've been together for more than two years), I
noted that she took roughly seven hours of saying "nothing" before
she finally spat out whatever was bugging her. The next time it
happened, I simply told her that I'd get back to her in seven hours
- she was startled by that until I explained the pattern that I had
identified, and it became our running joke. I don't have to use the
Seven-Hour Clock often these days, but she knows that she can talk
about what's bugging her whenever she wants to. The point is that
if you don't get an immediate answer, don't apply pressure - she'll
just clam up if you do.
4) Going back to point 1, look past what each of you is saying, and
try to identify the ways in which she expresses herself. You may
just find that she is indeed showing that she cares, simply in ways
that have escaped your attention.
All the best!