What Causes A Nipple Lump With Hardness And Immobility?

for 2 weeks my nipples were extremly sensitive and erect. that faded. i have small breasts so as i was feeling my nipple for any abnormalities i found a hard pebble like lump to the right of my nipple. it does not move, and its not painful. should I be concerned? breast cancer does not run in my family but ovarian cancer does. please give me some insight on what this may be. thank you