I had two times in my life of spontaneous breast growth. Both times, the nipples were the first things to show the growth. One of those times was in puberty when my hormones didn't know which way to turn. The other time was from a rapid weight loss which releases estrogen into the body. Sad part of the story is that neither time was permanent, and HRT only yielded slightly better results.
But, nipples can also change due to cold, stimulus, etc.
Wait and see what happens?