Though you don't mention it, statistically you are most likely to be a female. If you have what I think it is, it is called a "precordial catch" and is a sharp pain under the breast, usually on the left. When it occurs, it is painful to take a breath. I discuss this syndrome on page 44 of my book Chest Pain When and When Not to Worry. The book is available online from Amazon or Barnes and Noble in both new and used (inexpensive) copies.
In any case, it is a benign syndrome and falls into the "not to worry" area.
Please be aware that I am unable to diagnose medical conditions online.