Welcome to the Back and Neck Community. The members are here to provide assistance and support to individuals experiencing symptoms related to possible cervical and/or lumbar spine conditons. The advice and support provided is non-professional in nature and is based primarily on personal experiences. Should you require more professional advice, feel free to post on the Expert Forum and one of the medical doctors will be able to assist you as appropriate.
Shoulder blade pain as described in your post can be caused by several things. The fact that it seems to occur primarily when you are standing for long periods of time and does not occur with sitting, walking or even heavy weight training makes assessment of the pain more difficult.
Are you experiencing any associated neck pain or arm pain? Have you noticed any tingling or numbness of your extremities? If heat does provide good relief, it may be that you have a muscle sprain/strain that has not resolved completely. The only way to confirm the true cause of your discomfort is to obtain a medical evaluation and have the appropriate testing done to enable the doctor to provide a definitive diagnosis and treatment options. Schedule an appt with your doctor and post back with his clinical findings and we will be happy to assist you further.
Best wishes -----