Positive drug test but don't do drugs?????!

Ugh so apparently my OB thinks I do drugs now because I had a positive opiate screen. The lab mixes stuff up all the time I think that's what happened I'm flipping out!!!! I'm fighting this so hard and had another screen done today but I can't stop panicking. I won't even take a Tylenol let alone anything else. I am a med passer at my job so I am handling narcotics everyday but I don't take them!!!! They won't tell me what they are going to do tho. At one point they were thinking maybe my muscle relaxer was in still in my system (only took it because of a back injury) and I haven't taken it in 3 months. The way I look at tho someone who does drugs would not be fighting this hard to prove they don't. And when they said I could redo the test I was there within 20 minutes, not days to let anything out of my system. I just can't stop worrying ...