What Does Bump Under The Skin Of Right Breast And Delayed Periods Suggest?

Hi - I am 17 years old and found a bump under the skin of my right boobie. I just found it today and am a bit worried about it. I am involved with cheerleading but to what I can recall, I have not been hit in the chest or boobie area. Also, my period is about a week late but I was thinking that it was because of all the exercise with cheeer. What do you think it could be? What do you suggest I do about it?