Drug Screening - Testing Positive for Drugs I've never consumed

So I quit Codeine over 3 weeks ago and had a horrible withdrawal experience. They tried giving me Lorazapam, Diazapam and Seroquel to put me to sleep after I was awake for 5 days and had sleep deprivation. I only tried these medications for a day and that was 3 weeks ago.

Part of my recovery programme is I get drug tested every week. I keep testing positive for Amphetamines, Benzos and Marijuana. I have not taking any of these things except the Benzos but that was over 3 weeks ago for a day.

Can a doctor explain why this is happening? Because my DR and Councillor at my programme think I’m hiding more drug use when I am not. I also have a job interview approaching where I will have to be drug tested and if they get the same results I won’t get the job I’ve been looking forward to.

P.S I don’t even take vitamin supplements O.O