I have chronic pain a dull pain in my left arm elbow and upper arm from the elbow to shoulder on the outer part. Have had it for months.....?

Orthopedic eval. If you have not seen anyone yet i would start with your family doctor. Otherwise you may wish to see an orthopedic specialist.
Shoulder pain. Initial management of shoulder/arm pain should include nsaid's, ice, avoidance of painful activities. If no improvement, it may be time for an orthopedic evaluation. Location of pain concerning for rotator cuff pain.
Arm Alarm. Chronic pain of this type could indicate a herniation of a cervical disc in the neck, a possible vascular problem (such as a clot) or other peripheral impingement issue. It is worth obtaining an xray and/or additional imaging after a good examination by a physician. If you can't recall a specific injury and the exam and imaging are nonspecific, a metabolic evaluation should also be considered.