I dont like to read long long posts, so I will give a quick rundown.
College field trip for class, saw a girl from another class standing alone. talked it up, got her number. a shy girl, very quiet.laughed at my jokes. asked questions when I let the convo drop.
texted her same night saying it was a pleasure to meet her and to save my number. she replied all smiles.
the next day I call her, she is on the way to library to study, we talk for a minute and she asks if I want her to call me after shes done. I say cool. she doesnt call back, but she texts later saying shes so sorry and that she was studying all day and sleeping. I text back "you and me both

im about to pass out ill call you tomorrow."
which leads me to today. I am on campus. I shoot her a text seeing if shes around, she replies saying she wasnt and that she has classes in the mornings. I dont reply to this, instead I give her a ring 15 mins later because I was dicking around the bookstore.she didnt answer. I didnt leave a message. thats it
NOW
this is all in the span of 48 hours. I figure I will leave the ball in her court till wendesday, yes? My problem is im the type of person who wonders why she hasnt called back. I know females are flakes but when I like someone I call em back. its a superficial attraction at this point, but how should I go about this to get her out/on the line/communicating? I am aware of being overbearing which is why im cutting the calls for a couple days. am I over analyzing such a small period of time?
I have NO problems talking to girls after the initial number close. I just need to get her on the phone or out in person, I can handle the rest. Any help to make this work would be greatly appreciated.