What are the lumps under my nipples for and why do they hurt???

ANDY'S ANSWER: You have started puberty and your hormones have triggered one of the first signs - breast budding. It's where the breasts have begun to develop fatty tissue and milk ducts start to mature. As things swell and get stretched out, the nerve endings can be tender. You may find that wearing a bra for support and taking ibeprofen or acetaminophe will help alleviate the pain.