Why won't my recent girlfriend talk to me anymore?

At first, we would talk and text on the phone all throughout the day. I arranged for her to come over to my house at night a few days ago, and she did. Well we watch a movie, snuggle up, and close to when I had to take her home, she looked me in the eye, and we kissed intimately. Then the next day it just goes blank. She wont call or text me hardly, and when she does it is short, meaningless conversation. I try to arrange a date with her later, and she says she cant this weekend (which she may have a legitimate excuse but it didn't sound like she had anything going on). It's been this way up to now. What could be the reason for this? She tells me she still likes me and she showed it too that night.