I'm admittedly a bit of a hypochondriac, but I am concerned about some
twinges I've felt.  I'm going to have a full medical exam next month,
but in the meantime, I'm worried.
 I feel them mostly in my upper chest area, and my left arm about an
inch below the elbow.
 And my neck where it meets the shoulders feels a bit oddly sore.
 I'm worried about a lymph-related condition.
 One thing I've noticed is that these sensations aren't constant, that
if I'm distracted sufficiently they diminish or go away.
 Also, those areas aren't painful, just twinging.
 And in addition, when I feel stressed out, the sensations get worse. 
Relaxed, they diminish or disappear.
 I'm worried that I have a lymph related problem, but I also see a
stress connection.
 To help put my mind at ease, what non-fatal conditions could cause
these odd twinges and aches?

The first possibility that springs into my mind is fibromyalgia, which
can cause twinges and aches, and is often strongly stress-related.

In my experience (as a postmenopausal woman), transient bodily
sensations of this kind tend to become more common as we age, and (in
the absence of medical evidence otherwise) it is often best to make an
effort to avoid becoming obsessed with such things. Older bodies
develop their peculiarities, like older houses that creak in the night
or older automobiles that do odd little things, but continue to run
like troupers.

Take comfort in the fact that, although something may seem different,
that does not necessarily mean that anything is medically wrong with
you.