Is this normal?

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Im new to bfing and my milk is just coming in so Im not really in tune yet with what things feel like yet. Under one of my armpits feels really lumpy and slightly sore. Im thinking its just part of engorgement since my milk is just coming in but its only on one side. Should I feed her on that side next time to relieve it? Its the side she fed last on though so normally Id do the other side.