it happend again today. it only happens once a day....it lasted like 3 seconds...it was under my left breast but i could feel it's sharpness in my back as well...

im so scared...im justr 19 and im thinking this is my heart. today when it happend i was pretty relaxed, sitting down at a family birthday party after dinner, and i got up and changed seats and when i sat down...a miniute later, BAM...3 seconds of this sharpp pain right unnder left breast...