This injury is common among women who carry heavy purses, and servers who carry heavy trays of food. Keep in mind that this may be anything but usually it is strained muscle fibers. The sub-scapular muscles of the back are not hard to irritate. Do a quick evaluation of possible things you could be doing to upset it. Purse, heavy groceries, driving with one arm for an extended period, once you know the problem you can fix it. For now, drink water, take an ibuprofen, and get good sleep tonight.
