I have sharp pains under my left breast and a little to the side towards my armpit. could this be breast cancer?

Unlikely : In general.. No.. Breast cancer is typically a painless palpable lump or it's a mammographical painless finding. Inflammatory breast cancer is an aggressive variant that can be painful as it involves the skin. Advanced cancer that has grown into the skin or chest wall can also be painful. See your physician for a good history and physical. A mammogram or ultrasound could be indicated.

Get checked out: You are young but workup needs to start proper screening with self breast exams looking for new lumps, breast exams by your physician looking for skin or nipple chanes as well as masses or lymph nodes, and mammogram and ultrasound if needed are the best ways to pick up early stage breast cancer before it causes any symptoms. Once advanced it can cause many different symptoms throughout the body.