Job Update/Vent

I'm so frustrated and confused. I applied for this job at the end of June. I got my first interview in the beginning of July, then my second interview a week later. At my second interview, I filled out all the paperwork, the W-2, the direct deposit info, etc. I was told that I'd be called back the following week to set up my drug test and physical. I didn't get called back, so I finally called them and went in for the tests. Everything went fine, I was told that I'd be getting a call after the results came in and then I'd be able to start working. They said the results normally take about 2 business days. Since it was a Thursday, I waited til the middle of the following week to call them back. They said that my application was at corporate being reviewed. What?! Why is my application being reviewed when I already have the job? I thought I was just waiting for my drug test results (which of course are negative, I don't do drugs!). I called back today cuz I still hadn't heard from them and was told to call Human Resources. They quickly gave me the number and hung up. I called Human Resources and left a message. If I already have the job, and all I need is a uniform and start date, then what is taking so long? Why am I now not even sure if I have the job?