It could definately mean that your breasts are growing, or maybe just that you are expecting your period soon?
I am 19 and was sure that I had a lump in my breast, until I saw a doctor and was told that I am just feeling my ribs! It was very embarassing.
If you are too worried see a doctor. I don't think you need to at all. But you can just go there and get them to show you the right way to check your breasts for lumps so you know for yourself what is normal and whats not.