What Causes Breast Pain With Yellow Discharge?

my wife aged 39. last child is 12 years old. 2 months back she feel slight pain and slight discharge from one breast. now she consulted doctor and doctor told us that clinically NAD. then she advice us to go for mammography. after mammography doctor took her for ultra sound scanning. now we are waiting for the results. pain like a dot pain and it feels only when she pressed on breast. normal stage she does not feel any pain. discharge like yellow thick and only can see when squeezing. pls let us know what is the reason