Please have your vet perform a needle or complete biopsy of these lumps. They may just be mastitis, which is an injection of the mammary glands or it could be something more serious such as breast cancer.
I'm not the Vet...She will answer soon....What your describing can be anything from an infection, Mammary Gland Cysts to Mammary Gland Tumors...Your girl needs to have a Vet diagnose her (And treat) before these get worse....