Unexplained Chest Pain?

I went to the ER today because for the past few days I have been having these sharp chest pains, they last only a second and it feels like a shock or stab. They did an EKG, chest Xray and blood work, but found nothing. They sent me home with Ibuprofin and told me to follow up with my regular doctor. These pains come and go, last a second and I can have 3 in 5 minutes or 1 about every hour, nothing makes them more intense or worse. They happen when I'm busy and when I'm relaxed. Has anyone ever had this before?