Sometimes a milk duct clogs, causing milk to back up. Since this condition can lead to infection, it's important to try to remedy it quickly.
The bext way is to offer the affected breast first at each feeding, and to let your baby empty it as completely as possible. sometimes you need to help by messaging (or even compress ) the lump while your baby sucks.
Keep pressure off the duct by making sure your bra is not too tight, and by varying your nursing positions to put pressure on different ducts.