Pain In The Chest While Laying On Left Side. Pulse Increased. Reason?

I have had a consistant mildly sharp upper left chest pain (above breast ) for 2 nights while asleep and laying on my left side. It wakes me up. It tends to go away when I turn to my right side and almost completely when I m on my back or standing up, but comes back immediately when I turn back onto my left side. It has remained slightly since I have been up this am. There is no radiating pain, shortness of breath or pressure. It is not burning over sternum. I do have a functional heart murmur and have experienced PVCs which causes coughing in the past. My pulse is racing a bit but I think it may be due to anxiety from the pain. I have had normal EKGs in 2007 and 2009 for preop testing and they were normal plus a normal ultrasound of the heart in 2009 for fainting due to dehydration and to r/o heart problem. I have not done anything strenuous except to go on a 3 miles walk. I am a 64 1/2 yr. old female, 5 , 8 at 178 lbs, mild hbp under control with meds., all bloodwork wnl. What do you think it can be?