What Causes White Pus Discharge From Nipple During Breastfeeding?

i had a baby 9 months ago but had to stop breast feeding when about 8 months ago. i have started having a white puss discharge coming from my left nipple only and if i squeeze it it almost like pusses out and sometimes blood comes out. the only reason i squeeze is cause it hurts and that relieves the pressure. i have had my primary give me a breast examine and he doesnt feel anything abnormal. i am scheduled for a breast ultrasound tomorrow but i am really nervous and wondering what could be causing this? i have started an antibiotic incase its an infection but its still happening. im worried because i have read it could be a sign of breast cancer. thank you for your time!