In my years at the clinic I have seen many cases much like the one you
describe so much so that  "Have you ever injured your breast?" is now a
permanent part of our history taking.
Seat belt and steering wheel injuries are most common. Blows to the chest can
occur in sports or simple rough housing. Usually the mother can identify an
incident  involving her breast that hurt "for days".  A horse kicked one mom
when she was a teenager. When her milk came in you could see the outline of
the horseshoe imbedded in her breast.
In these cases it can be assumed that the ducts were crushed, hence the
trapped milk resulting in tenderness, redness and swelling. If the ducts were
crushed, it can be assumed there is no outlet for the milk, which will back
up behind the injury. It seems that the milk will remain sterile if there is
no inlet for common bacteria.  Most of these mother's do not have mastitis.
They remain afebrile.  What we do is selectively "dry-up" that portion of the
breast. Cabbage compresses, ice and no extra stimulation to that area. Our
mom with the horseshoe took several weeks before she was pain free. But she
continued to breastfeed. She never developed mastitis.
I have serious concerns about the multiple courses of antibiotics.: What good
are they doing? Are they really needed?
Marie Davis