What Causes False Positive Test Results For Benzodiazepines?

I am in a outpatient rehab and have tested positive for benzos . I have not taken anything but my prescribed meds which include: fluoxetine,risperdone,clonidine. i have also take tylenol pm, delsym cough medicine and tylenol cold and cough. could any of this caused apositive drug test? They have kicked me out of program,but i have not taken anything not prescribed