I had the same problem and did all the on-bike exercises to make it feel better as I rode. Then I read somewhere that if your bar is too narrow your upper spine and lower neck will hurt; if your bar is too wide the outside of your shoulders will hurt. I went from 42cm to 44cm to 46cm and finally to a 48cm drop bar from Rivendell. My shoulders are 44cm. No more pain so I can concentrate on the ride rather than the pain. Looks a little less than race oriented but I'm not the one rubbing my shoulders and neck after a ride.