Dear Natty S,
does it look like pus? is it cloudy or clear? is it sticky? does it smell bad or have no odor at all? is the local area red or warm to the touch?
if you have been romantic with a young man (I am assuming you are a young woman) it is possible you have a little infection from germs from his mouth. If that is the case an antibiotic would help.
it might be breast milk. sometimes the pituitary gland goes crazy and makes prolactin and oxytocin when it shouldn't, and this can cause your breast(s) to make and let down milk. for this you need to see either an ob-gyn or an endocrinologist.
it could be many other things as well. without seeing it, no one can tell you exactly what it is. breast cancer (such as ductal carcinoma in situ) is on the list but it would be far more common for it to be something else. I only mention cancer because you are posting on a cancer web board so perhaps you think it is cancer (i don't think it is but like i said no one can tell you much without seeing it).
i wouldn't worry too much about your mum or being embarrassed. there are much worse things in life. talk to your mum is my advice. if that is just out of the question, is it possible for you to make an appointment with a doctor? an ob-gyn doctor might be the best at examining this area and making you feel comfortable. find a female ob-gyn doctor.
a warm moist washcloth placed over the area may help a little but is no substitute for antibiotics if it is an infection, and is certainly no substitute for a proper diagnosis for that matter.
in any event don't be embarrassed, talk to mum, get this taken care of, be well, and keep us posted.
Hugs,
-Amnia