I have been having pain for about three weeks now, at first it wasn't so bad but the more it is progressing the worse it is becoming, in the direct middle, right below my sternum and even under it. At first I thought it might be gas or heartburn, but I know what both of those problems feel like. I have heartburn at least once every other day. When I hold my breath I experience a terrible pain on the right side chest, middle, and a little on the left side as well. Just a side note, I have been taking Amoxicillian 500mg for about a week now for an infected tooth. What could be wrong with me. I usually wait until I can't stand it anymore before I go to the doctor's office. I am almost at this point.