I Had A False Positive For Amphetamines. I Am Prescribed

I had a false positive for amphetamines. I am prescribed trazadone, Harvoni, hydroxyzine, propranolol, suboxone and gabapentin. It was a saliva test that I failed but I passed a urine drug screen the night before. I took another urine screen the day after the swab test that I failed and waiting for the lab results. I started the Horvoni the day I received the saliva swab test and felt weird. What could have caused the false positive.