I Am A Surviving Pancreatic Cancer Patient And Am Dealing

I am a surviving Pancreatic Cancer patient and am dealing with Chronic Pain. I take my medications as prescribed and also use St. John's Wort (Goat Weed), Echinacea and Goldenseal herbal supplements. The last two urine tests that my Pain Management Doctor administered came back positive for THC. I do not use marijuana and got fed up with the results so I went to a separate lab and had my blood drawn. I've had tests come back positive for Heroin but that was due to my Doctor Prescribing a high dosage of Morphine. So what I am asking is wither or not taking my regular pain medication in conjunction with herbal supplements can create a false positive for THC?