Clogged duct. You can spray hot shower on it, massage gentle to express the clogged milk and let it flow out. Also can try pumping in high suction and massage mode. Take lecithin to help Thin your milk too so it can hopefully flow out. If nothing of the above mentioned is helping, get a breast masseuse to clear for you. There are a few that can visit your house to do it for you.
I have it multiple times. Clogged duct at the areola. Keep pumping / latching. And lecithin FTw
you probably got a clog duct. Just massage slowly will help to clear ....