So I Have A Ache Behind My Left Breast And

So I have a ache behind my left breast and yesterday I had a bad pain down my left arm....It was not numb but it was weak for about 1/2 hour. I thought maybe it was a pinched nerve so I went and had a massage the pain did subside. Until about 2 hours ago when this ache started happening. I took an antacid and 2 ibrophen and have been laying down and drinking lots of water. The ache is not getting worse but it is not letting up either. Any ideas?