Suggest Remedy For Pain In Left Arm Below Elbow

i have pain in my left are below my elbow. it hurts to pick up the milk out of the refrigerator. it hurts to bend my arm up toward my body. it hurts to bend it back out from my body. it is not in the elbow. it feels like the muscle on the outside of my are is so sore. i swim most everyday trying to get it to stop. i can push against something, i just can't pick up anything without it hurting.