
Mastitis is an infection and inflammation of the mammary gland, and can happen at any time during lactation, whether following pregnancy or false pregnancy. If caught early (by ensuring a steady flow of milk to remove the pressure) infection can be avoided. But if it's left untreated, infection can set in, requiring antibiotic treatment, and the pups removed and handreared. Basically, it's best to ask for veterinary advice sooner rather than later.