What Causes Pain In The Side Of The Breast?

Hi I am a 47 year old female and for the past 2-3 weeks I have had a throbbing pulling type of pain in the side of my left breast I had a hysterectomy 4 yrs ago I am not dur for a mammogram until may could the pain be heart related or is it something else it comes and goes somedays it doesn't bother me so much I want to workout but am nervous, if it is my heart I have no health issues or heart related illness and am on no medications at all. Tina