Random strain contained by my breasts?

Recently I've started to get pains within my breasts. It's always solitary in one breast and it's other on armpit side of the breast but it alternates so sometime it'll be in the moved out one and at other times in the right one.
The affliction also varies from a sharp shooting misery to a dull (but still very definite) spasm.
I know I'm not pregnant on account of I haven't missed any of my period. I am in the middle of my cycle. Also if I touch my nipples they are slightly sore.
I be just wondering what this could be cause this? Depending on your age, it could be that your breasts are growing. I had breast backache and went to my GP more or less it, and she said it was simply from getting elder and developing. It could also be because of your period, resembling getting cramps but in your breasts.
If not that, after it might be a good notion to get checked out, and take home sure it's nothing serious.
it could be that mode from change of diet, stress, exersize.. anything. If it keep up more than a week then acquire it checked out. I get heart burn alot and im solitary 15.. its from the way i diet and excersize...