I have discharge from the nipples
every month with
my period. I, like you have been tested several times, and my doctor has no explanation except it's caused from hormones. Make sure to squeeze, and get it out, check it regularly, it's gross I agree, but I've had this since my second child 4 years ago, and after a hysterectomy I still have discharge. If I do not get it out in time, or it's stuck with pain to squeeze it will turn green, meaning infection, usually mastitis.