What Causes Pain In My Breasts Days Before Onset Of My Menstruation

hello , there is pain in one side of my left breast .pain goes and comes , i notice it more when i bend down.my periods are due in next 2-3 days . Is it related to it or is there some heart problem as only in left side of my breast. it has started now from my last month period. i had a baby through normal delivery in jan,. he expired due to jaundice within 4 days. is it connected with hormonal changes . please guide me