My DD is 8 mo, still nurses a LOT. The other day I noticed this weird white blister thing in my left nipple, like it's a milk duct that's swollen. My breast isn't red or swollen like mastitis. I tried to pop it but I couldn't. I tried putting Lansinoh on it and nursing a lot on that side, and it went down, but is still there. What is it and how do I make it go away?