Girls, hi ? I noticed this morning that a lump formed in my underarm a…

Girls, hi ? I noticed this morning that a lump formed in my underarm and it's not letting me lift or move my hand (it turned out that the milk went away and a lymph node was formed - I don't know the exact name) now I'm afraid of getting mastitis What should I do? How to remove it? Who has experienced this? I'm trying to relieve myself by expressing, what else can I do?