You go to a gynecologist each year for a pelvic exam, right? Talk to your GYN about your family history and your lumpy self, and see if s/he can help you figure out which lumps are normal and which aren't.

That said, if you find a lump that doesn't go away with, say, a new cycle, or that feels hard or actually distorts the outside of your breast...go have the GYN check it out.