C17, Notification for interviews is done by E-mail. Make sure that whoever you use isn't filtering out Southwest as spam, etc.

How much TPIC do you have? I know of a few guys with the HPA type without enough PIC that haven't been called.

I'd also go back over your app top to bottom to make sure ther aren't any mistakes. Otherwise don't sweat it to much, it's December and things slow down in the training departments right now. They may also already have enough guys in the pool for Jan-Feb. Guy I work with that intervied in August (and hired) hasn't even gone to class yet.