I sometimes have numbness and pain in the center of my chest. i've been to the er, but all seems well. what's wrong??, could i have costochondritis??

Certainly: It certainly could be costochondritis - stress, viral infections, muscle pulls can all cause this condition and it is very painful at times. As long as it has been shown that your heart and lungs are normal then I would suggest seeing a chiropractor for treatment. NSAIDs also are helpful. It is also possible that you are having esophageal problems - talk to your FP about that as well.