I took an xray.yesterday at the er and found nothing in my chest. i still have pain in my right chest when i breathe. what can it be?

Many things.: If you're still having chest pain, you should return to the er. Many serious things such as pulmonary embolism are not seen on a chest radiograph. That being said, the are blood tests which can exclude that possibility.

It could be any: Number of things, but if ed doctor did not find anything, it probably is something self limited. Possibilities include occult injury, pleuritis, or shingles. Pulmonary embolism is unlikely if ed doctor wasn't concerned about it. Follow up with your own doctor if pain persists.

Pain producing sites: There are a number of sites in and on the chest that can generate pain. The lung itself has no pain sensors so having clear lungs, while relieving would be expected at your age. Depending upon the location and quality of the pain it could be muscular, or inflammation of the joint between the cartilage and bone of the rib, or inflammation of the pleural lining of the lung. Need more information.