You should have your Mom/Dad take you to the doctor. Don't be embarrassed. Bodies come in all shapes, sizes and colors; they are all magnificient in their own right. Love yours and thank it daily for everything it does for you...walking, breathing, seeing, hearing, etc. The important thing is to go to the doctor soon.
First let me say that you should NOT be embarrassed to go to your Dr. about something like this. Dr.s see problems like this every day and can explain in detail what is going on within your body. In your age group a lump like this is fairly common and is usually attributed to the hormone changes that are naturally occuring in young bodies. Please do ck. with your Dr. to put your mind at ease about this and also to learn of other things that may be happening in the future, OK ?? Take care ......