Trouble Breathing: Anxiety or Medical Issue?

Hello,

I have been having problems breathing for quite awhile. Only now it has progressed to the point were it is extremely uncomfortable. I'm experiencing fatigue, dizziness, tingling in hands, head aches, shortness of breath, and some pain right underneath my sternum. I can never get a full breath so what I do is I try to yawn. Sometimes that usually will help. If I push with my two fingers inward right underneath my sternum, I feel a bump of some sort. It kind of feels like scar tissue, but not sure what it could be. I went to emergency because I was having problems breathing. They took x-rays of my chest and came up with the conclusion that it was anxiety. When they gave me my diagnosis, I was almost sure that they were wrong. I have deep concern and am affraid that it might be something worse than anxiety. I asked the doctor if they could take some blood test just to be on the safe side, but he refused and told me just to go home and relax. He gave no prescription, but did say that if I wanted any tests to be done that I would have to ask my physician to do it. The problem is that I have no physician because I have no insurance. I would have to go to a clinic of some sort, but I just want to know if you might think that there might be something there more then just anxiety. Also, what you might think could be the problem.