What Could Itchy And Tender Breast Nipples Indicate?

Hi i've had strange sensations in my left breast for a year, it feels sometimes sore,sometimes itchy ,sensitive, tingly and a tender nipple which becomes erect frequently and feels like its being stimulated. I sometimes have a feeling like the let down sensation when breast feeding. There is no change in the appearance of breast or nipple and my breasts are naturally lumpy. Doctor examined me a year ago, didn't find anything. I'm 45,what could this be?