1. The reason is related to one's psychological state, such as serious anxiety and sulking. When you are young, it will happen if you are lovelorn and hit too hard.
2. You can use Chinese medicine to get through the meridians of the whole body and discharge garbage. Nothing serious. You can also make it disappear through more friction.
3. If you are angry, will it increase? Generally, the armpit will increase. It's okay. Don't worry. It's okay after ten years. Also, was this lump naughty when I was a child and hurt my chest, which led to bone healing or hyperplasia? I can't find any other reason.