Arrhythmia and Stress Realated Palpitations

I am a 27 year old female. I have been suffering from an stress and anxiety disorder sine I was a young girl. About a year ago, I found out that when I am under a lot of stress, my blood pressure starts to rise. I recently had an experience that caused so much stress, that I began to have chest pains and a strong headache. I went to the ER and they said that my blood pressure was elevated and gave me a "Velvet Glove" because they felt that the chest pain came from stomach problems. They gave me a narcotic which caused my stess level to go down and therefore caused my blood pressure to go down. When I first came in, they did an EKG. The ER dr came to me and told me that everything looked fine. The next day, I got a call from a Cardiologist that saw my EKG. He told me that while I was in the ER my heart was in Bigeminy. He said he was concerned about what my heart was doing on a regular basis. He had me do an echocardiogram and a 24hr Holtor Monitor. When I saw the Cardiologist, he told me that my heart showed that I have an "Extra" sinus node that causes me to have an extra beat in the lower cavity. He said this happened about every 10 beats (give or take). He has me doing a Stress Test to see if that causes my heart to go into Bigeminy. My question(s) is/are: Since this was the first time in my life that I have ever had an EKG, could this have been happening my entire life? Should the ER Dr have said everything was ok when my heart was in Bigeminy? How can you tell the difference between stress related symptoms and the effects of a PVC? My chest occasionally hurts as does my head. This usually happens when I feel very anxious. Also, I have pain in my left shoulder area (very sharp and it lasts around a minute), could this be an effect of the PVC?