Sharp constant pain above left breast near corner of armpit? i do exercise 5 days a week and didn't have the pain this morning. started 1 hour ago.

Strain: Given absence of acute event such as "pop" or "tearing" sensation likely represents simple muscle strain and should get better with time. Avoid provocative activities in the gym, consider ice if particularly painful and of course anti-inflammatories like advil, (ibuprofen) motrin.

Might be a: pectoralis major muscle strain from workout injury -- esp. if worsen only with arm movement. But remember to do your usual breast self exam, checking all quadrants etc. And discuss with your doctor if this is persisting. Try a NSAID to see if it gets better. Also cardiac origin to this although not as likely is important to rule out if symptoms still present. Discuss with your primary care doctor.