Hi Desire: At your age, it's perfectly natural to feel lumps, soreness, and pain in your breasts; they might even just feel, well, "different" than they used to. This is all natural. You're going through puberty, and your hormone are working overtime. This process produces changes all over your body, but especially in your breasts. At your age, statistically speaking, your risk of breast cancer is 0%, so please don't worry too much about that.

I'd suggest that, if your left breast continues to bother you  for another few weeks,  or becomes worse (more pain, more constant pain, more lumps), you should see a doctor, just to get checked out and have a chat about what's going on. Again, it would be nearly impossible for you to have breast cancer at age 15; but that doesn't mean you shouldn't see a doctor. It's better to be informed about what's going on, then to simply be afraid. Good luck - PJH