Help me get my girl back?

So my pseudo girlfriend is acting really funny lately and I need help reading her. I've known her for about 6 years, and flirted for about 3 of those. We've recently gone out on 2 dates one of which was my prom. At any rate she seems to have a great time w/me and we get along great. The main problem I have is that she recently just stopped returning my calls and messages. I want to know how to fix this,help?