Why would a girl do this?

So I met this girl a few months ago, asked for her number and she gave me it. Text A LOT for about 2 weeks, eventually asked her out for dinner, she said yes. It went really well, she said she wanted to see me again. We meet up 3 more times, every time we met up it went really well, says she really likes me blah blah blah, we end up kissing on the fourth time. However after this we start talking less, her responses are shorter, she even took up to 5 days to reply to one of my texts. I don't hear from her for about 3 weeks, but she suddenly invites me to a party she's going to. I agree to go, we basically spent the whole party just talking to each other. I tell her to text me whenever she's not busy and we can arrange to meet up and do something (this is where i think i mucked up). That was 2 weeks ago and she hasn't bothered to contact me? I really don't understand...