You say you haven't done anything wrong, but it sounds like she might think you did. If it were a matter of not having anything in common anymore, I imagine she would still be civil and give a distant smile and 'hello' when she saw you.
Perhaps it wasn't something obvious - maybe you didn't get into a huge fight. Maybe she didn't bring it up. But you could have offended her, scared her, or annoyed her in some way. The truth is, by trying to contact her so often, you are just making it worse. Whatever problem she had before, she probably thinks you're annoying and needy to top it all off at this point.
Others say you should talk to her. I think you need to do one of two things:
a) Try to get her to talk. You need to find the right way to do it, because if you try to do it the wrong way, she can easily ignore you and you won't get answers.
b) Just ignore her and try to move on. It's hard, but it seems like she is trying to get a message across that this is what she wants.
Worst case scenario: she continues to ignore you and not answer your questions and you don't talk again.
Best case scenario: You find out what happened and it all turns out to be a misunderstanding and you can try to patch up the friendship from there.
Good luck.