Is the actual lump sore? When I had a blocked duct, the area around it (a whole quarter of my bb) was excruciatingly painful and it had a bit of redness to it. I managed to get it out with constant feeding and quite firm massaging (nearly passed out from the pain but didn't want an abscess or mastitis!!). If it progresses to mastitis you'll know pretty quickly because the pain is still there but all of a sudden you feel like absolute shi'te, really tired, achy and fluey. I hope it's not a blocked duct but if it is, it should be easy enough to get rid of with massage. Heat packs help too. Sorry that this bf journey isn't enjoyable at the moment. You know my stories so I understand the frustration. You are doing a great job.
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