What would/could cause a False positive & False negative on Drug Test?

[mel6801]

I take Hydrocodone 10/500-4 times a day, Soma 350mg-4 times a day, Celexa 20mg-once a day, Lipitor 20mg-once a day, Enjuvia 0.9mg-once a day, Motrin 1600mgs a day, Asprin 350mg-4 times a day, all these everyday for over a year. I had to take pain management urine drug test and it tested positive for Benzodiazepines and they said my Soma didn't show up at all. What would cause this as I never take anything but what the doctor has prescribed me, and I ALWAYS take ALL of it like I'm suppose to. Can any of my meds cause a false positive for Benzodiazepines and why in the world wouldn't my Somas show up, since I'm sure that would be one of the drugs they would be looking for.

Can anyone help me out here on what the deal could possibly be?

[Peanuts2]

Why are you in such pain?  Why are you on all of this poison?????  Go back to basics.  Clean your body of chemicals.  Go to health food store and get pH test strips.  Anything lower than 7.3 means your whole body is acidic and disease runs ramped in an acidic body.  Start detoxing.  You'll watch your life go down in a downward spiral if you don't start paying attention to what you are doing with it right now....if you get a toxic liver, there is no test for that.