I started getting breasts when I was about to turn 12, but they don't really show up and they are shaped like triangles. Yesterday I had my first period and after that I noticed my breast are getting bigger. It used to not show up so I never wore a bra, but now they are getting rounder. I also notice the dark skin around my nipple is expanding and it now hurts to run. Is this normal after you get your period?
Your periods are a reflection of hormones changing in your body. There is a sequence that takes place in an adult woman's body to cause menstruation. But these hormones don't just affect your uterus. They also affect other parts of your body and your moods as well.
One common result of menstruation is that most women complain that their breasts get very sensitive just before their period begins. The feeling is described as tender or almost feeling bruised. The changing hormones may the nerve endings in your breast more sensitive at certain times of your cycle.
You may wish to consider wearing a sports bra when you run. This type of bra holds the breasts tightly against the body so they don't bounce as much when you are running. The less movement translates into less sensitivity.
As you continue to develop, your breasts will continue to get rounder and more pronounced. Where you could get by without a bra, in the past, you will likely find wearing one to be more comfortable. So let your mom know it is time to do some shopping.