Is my girl friend flaking?

I've been seeing a girl for the last couple months. We were talking and texting every day for about 6 weeks and were seeing each other about twice a week. Then she went on a vacation with family. While she was on vacation, our relationship seemed to get stronger. We both shared strong feelings we had for each other and couldn't wait be back together. But as soon as she made it back, her feelings seemed to change. She was less eager to see me after she returned. Her replies via text were more standoffish. I have no idea what happened. We have only been together once since she returned, and she seemed a little nervous. Don't know what happened. Before the trip we were growing closer, while she was on vacation, we were even closer. The text messages we sent were more pionate than ever before But now she is so distant. I have messaged her asking what is going on and now she won't even respond. She hasn't talked to me in about 5 days. I'm really confused. I keep guessing what the heck she is thinking about. She isn't great at communicating, which leaves me guessing. We aren't teenagers, this isn't puppy love. I'm 33 she is 28.