Hi I've Been Experiencing Chest Pain Everyday. Recently It'sbeen In

Hi I've been experiencing chest pain everyday. Recently it'sbeen in my upper back too. I'm very worried it could be my heart. About a month ago I had an ekg, heart monitor, blood work and a chest xray and everything came back fine but I still worry. My doctor said it is most likely muscular pain and anxiety rather than my heart. But why does it come and go and why does it hurt in the middle of my chest when i take a deep breath? Its been persistent everyday. And it makes me worry. I'm only 21 and have a 2 year old. I really don't want any heart problems