There are certain everyday things you eat that can cause a false positive test for varying drugs. There's a thread on here somewhere that lists them out.
I suppose you can ask for an oral swab test. I believe they're more accurate.
However, if you are doing any other drug (occasionally), like heroin, commonly the drugs you mention are mixed in with what is supposed to be heroin. So in that case, you would be getting a positive test.
Since the drugs you mention stay in the system longer, it would cause a positive test for those and not other opiates.
i take nexium for reflux; effexor xr for depression; and reglan for digestion all of witch the clinic says will not give a false poss.
are you on any other meds?
Are you taking soma ? I would ask for a blood test