dull ache in my left chest and breasr...all test normal what could it be?

have been feeling this weird ache and pain in my left breast and chest....for a week...... i am 20 yrs old.... i had been feeling this symptoms since last year.... and last november.... i felt this hypertension....or anxiety attack i cant really explain and i felt really sick..... the ache that im feeling in my chest part...is although bearable still i felt very uncomfortable....and very frightening..i also felt the  pain in my back....the upper area and sometimes also felt the pain in my arms... or into the other breast....  i consulted my doc and all my test are normal...including ecg's and my xray.... but i can still feel the pain...he said that i only lack exercise and i should change my life style. he gave me some meds and after a week im back to normal again...but this week the pain returns..... so im really scared...my family thinks im just thinking that i have a disease but in truth i have none...but i really think otherwise...because i can feel my own body...pls...can anyone answer me??what should i do.... i dont have any family members or relatives that had  heart problems....so i dont have it in my genes. or maybe my breast is only growing? or maybe i only have muscle pain aches in my chest?