What Causes Pain And Pressure Under Breasts And Excessive Sweating?

I have had a pain under my left breast that feels like something is pressing under my breast. I am 76 years old. At night I have been breaking out in a sweat around my neck and in my chest. Usually it subsides when I take a nerve pill but returns about an hour. It has been happening on and off for two weeks but since last night will not go away.