I've been have sharp short pains in my breast under my nipple and on the side and above and around my chest bone hurts what could this mean?

Inflamation: Some one your age ( 18 ) with symptoms you have most likely infection in the montgomery glands , that are around the areola .Apply some warm compresses and see your doctor , for some times needs drain the pus , possible antibiotics and to make sure you have no other problems in the breast.

Variable: It could be a breast cyst, especially if it varies with your period. It could also be in the rib, if here is a history of trauma. Get a good breast exam from your doctor.