Hi! I'm A 15 Year Old Girl And A Few

Hi! I'm a 15 year old girl and a few years ago I found small hard lumps in both of my breasts. I didn't think and urging of it since breast cancer isn't common in people under the age of 25. Recently I found that the lumps got bigger and are very firm. They are able to be moved around but the are sort of painful. Could this be something serious, or is it just something that will go away on its own?
Thank you!