What Causes A Painful Lump On The Breast?

my son its 2yrs and seven months old i breast feed him until last week because about 2 or 2 1/2 moths ago i've notice a lumb on my right breast at first i thought its was not a big deal.but for the last few weeks it started to hurt,my mom had a mastectomy on her right breast due to cancer, and my aunt(my mom's sister) also had cancer on her right breast.but as far as i know cancer don't hurt does it????? and i don;t have a primary doctor should i go to the hospital?????????????