Left Arm and Chest Pains

For about a week now my (27yr. f) left arm hurting and chest pains have been here. Before the arm pain was constant, but now since I have been tylenol for past two days it is just now in the joint of my elbow and then whole arm from time to time and down into palm of hand by thumb. The chest pains are from time to time since the tylenol has been taken. What is this? I know before when I thought I was sick, I stressed myself out. When MRI came back fine I had to calm my body down. It has been a complete month now since all this, now these aches are happening. My EKG said my heart looks fine about 3 weeks ago. The pains go through my back, to the front of my chest (left and right sides) through my arm and then its over. About 20min. it will start again.