Get Your Dog Care Questions Answered by Experts
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You still have one question to which you did not accept an answer.
Since you accepted this one instead, I'll go ahead and tell you what I think.
Some breasts are used more than others when mom is nursing so they will produce more milk. The larger the litter, the more nipples are needed to feed at one time. If your litter is small, this is pretty normal.
The hard breast is NOT normal and should be taken seriously. This can be a symptom of mastitis, a serious breast infection. If you suspect this, you should see your vet for antibiotics so that you can get it cleared up.
Until you can see the vet, you can use warm compresses to give her some relief.
Let me know if you have more questions about this. I would be happy to help more.