Girlfriend totally ignoring me after coming back from vacation. What does it mean?

So, my Girlfriend went out of town for the weekend to go to a wedding where she was to be a bridesmaid. She got back Sunday. At least I think she did. I'm not sure because she hasn't returned any of my calls or texts since then. Before she went out of town we were talking/texting all the time and couldn't get enough of each other and were even making plans to spend our birthday together since we share the same birthday (coming up next month). I'm totally confused.
Girlfriend totally ignoring me after coming back from vacation. What does it mean?
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