Hi Annie - Please don't stress about breast cancer. About 85% of all breast lumps are NOT cancer. And at your age, your chance of having cancer is 1 in 2000+. So it's not likely. You probably do have some fibrocystic changes connected to your period. Here's a good article on fibrocystic breast condition. You could also have a fibroadenoma, which are most comon in women between the ages of 20-30; here's a good description of fibroadenomas. Your doctor is being cautious, which is good. Once you find out what the lump is, I'm sure she'll discuss what you can do about it as well. Good luck! PJH