Yes, yes - I had a lump in my armpit for 2-3 wks after having my LO. It kinda freaked me out because not only was it fairly large and tender, I could also squeeze milk out of it if I pushed hard... made me wonder if I had an odd third nipple or something. But a friend who's an OB told me - just on the phone, so no actual observation - that it was probably just a swollen duct/node from milk coming in and that it'd eventually go away... and it did - a few days later.
Hope that's what it is for you and nothing more serious...