This does not sound like a galactocoele.  A galactocoele is usually
bigger, usually *not* painful, although it may have begun in a blocked
duct, and is usually deeper.

I'm not sure what this is.  My inclination, from what you wrote is to
open the skin on top of this and express out whatever is there.
Afterwards, clean, and apply antibiotic ointment (mupirocin?).

Jack Newman, MD, FRCPC