Hey, Susan! You have lots of good advice here, but I'll put in my two cents of hope. When I first started playing, I got concertina shoulder. I went to a physical therapist and he gave me some exercises to do to strengthen my upper back---they were no big deal, the hardest thing was remembering to do them. The pain resolved over about 6 months and never got so bad that I couldn't play. But now, I do try to watch my posture---it's so easy to hunch over the instrument and to curl your shoulders inwards. Also, when I play a tune I'm uncomfortable with, it's easy to tense up, when it would be better for my body and for the music, to just relax.
Deep breaths!
xo