If you were called for the drug screen you probably will not hear anything more from SWA until four weeks prior to your probable class date. The PD tries to call four weeks prior to let you shore up all loose ends, take care of any accrued vacation time, call in sick as many times as possible to use up sick time (did I just say that out loud?) and to basically give you a heads up. Two weeks out you should get a call from a CP with an official class date offer.
You may however get a call or two from the background check people to verify information or ask for more current numbers. If you get called for the P-Test, you're pretty much in the pool unless they find anything in your P or find out about the body you helped move during your last spring break in college.
Atleast this is the way it has worked for me and for the others I have heard from. I hope to see you there soon.