I recently tested postive for cocaine using a urine sample  i have never done 
the drugs what happened

Medications & Substances Causing False Positives


According to a report by the Los Angeles Times New Service, a study of
161 prescription and over the counter medications showed that 65 of
them produced false positive results in the most widely administered
urine test. Ronald Siegel, a psychopharmacologist at UCLA said 'The
widespread testing and reliance on tell-tale traces of drugs in the
urine is simply a panic reaction invoked because the normal techniques
for controlling drug use haven't worked very well. The next epidemic
will be testing abuse."

Byrd Labs has in its possession an internal document from the Syva
Company, makers of the widely used EMIT test. This document, leaked by
a disillusioned company employee, lists more than 250 over-the-counter
medications and prescription drugs that can cause false positives.

Cocaine - Substances or Conditions which can cause false positives
Kidney infection (kidney disease)
Liver infection (liver disease)
Diabetes
Amoxicillin, tonic water

http://www.passyourdrugtest.com/false-positives.htm