Female dog has had puppies.........?

I have a mamma dog who had puppies over 4 weeks ago-- all the puppies are weaned and the mammas teats are HUGE- I feel of them every day to make sure they are not getting mastitis and they have been soft and fine just very large and today i felt of them and they are hard - i can still squeeze milk out of them and they are not painful-the milk is a normal white color- but they are very very hard and i can feel the glands - what should i do-- are these signs of mastitis forming.. if so what do i do???