this happened to me twice in 3 days...i had a
UA at one hospital, i tested positive for THC, negative opiates and negative for benzos (i dont smoke pot and i do take a low dose of benzos) so my doc sent me to another hospital 3 days later, i tested negative for THC, negative again for benzos and positive for opiates...' she tested me herself the next day and i was negative for everything but benzos...LOL!
so it DOES happen...hospitals DO mess up...he should have retested you then...