I've had pain in my left shoulder/upper back for 3 weeks. Also, pain in my left upper arm, with some tingling/numbness. Massage helped some. Ideas?

Could be your neck. Have your doctor check you for neck problems which can press on the nerves going to the shoulder and arm. It could also be coming from a muscle spasm in he upper shoulder.
Massage and therapy. Try massage and physical therapy for muscle relaxation. Sometimes an anti-inflammatory or muscle relaxant can also be of some benefit. If no relief, you may want to consider an MRI of the c spine and left shoulder. Tingling may be due to some nerve impingement from the muscle spasms.
Brachial plexus. Need a full exam including an EMG to check your brachial plexus.