Mine too, this armpit has literally done a whole number of really odd and unusual things since I've been pregnant / breastfeeding. Who knew?! I certainly didn't and I think that added to my anxiety as I didn't expect any of it in my armpit! Once i'm done with babies, i'm planning to get the bulge & cyst removed as I don't like it.
I wish I had been like you and not been so self-aware when pregnant! Joking aside, it really does sound like you have nothing to worry about, it all sounds very innocent.