My dog has what it feels like is hard balls in her boobs. She had puppies 6 weeks ago, but hasn't been feeding them since 3 weeks ago. Is this normal?

Hmm sounds like you need to buy and study some books on breeding. Call your vet they will be able to tell you. I don't think that we have any professional breeders on this site nor do we have vets.

Yes, take her to the vet. She stopped nursing awfully early--the hard balls could be anything from mastitis to breast tumors. Infection in the breasts can sometimes occur along with infection in the uterus--a potentially fatal condition.

She may have an infection or clogged milk ducts, she needs to be examined by a vet right away, she should have a blood profile check ( esp. a Complete Blood Count to check for signs of infection, and a Calcium level)