Am I over qualified? If not is it discrimination? What is the issue here?

I have seven years experience. I am very productive with information from my previous employer to back it up. I applied for a position in my field with a major company. I received an automated message to set up an interview and did so. I drove 30 minutes to the interview site and arrived on time. I was told by HR that they weren't hiring and that they should have told me before I drove there. I was told that I should apply to another location as they couldn't conduct the interviews for another location. Two days later, the same job is posted again. What gives? I relocated from one state to the other and trying to stay in the same field as I enjoy the work. Not too many people in my field can use a Prosecutor as a character reference. 50 applications and one interview, I am getting very discouraged...