Try not to worry. The news say everything causes cancer and they want us to worry about everything! I get them too. All they are is spots under the skin. They'll go away after a few days. It's just where your pores are blocked... Go to the doctor just to get them checked out. But I don't think it's anything to worry about :) xxx
Do they feel like small hard lumps? These are fairly normal. I used to get them under my arms from time to time when I was younger, and when I stopped using anti-perspirants they went away. They usually last several weeks and felt like a pea or a grain of some kind under the skin. There is no need for you to worry about breast cancer at your age. You will be fine.