I've had muscle spams (feels like a baby kick) on the left side of my sternum about 1 inch under my breast. occurs: 10-20 min intervals. ?

Well: At your age its unlikely cardiac, but if you get nausea, sweaty, short of breath, consider your heart is under there. It could be secondary to a strain if there are changes in pain with berating. If musculoskeletal, aleve (naproxen)v2 2 ti, es per day should help. There is the remote chance of esophageal spans or another one called costocondrits. It sounds muscular, try aleve (naproxen).