What Causes False Positive For Methamphetamine In A Urine Test Report?

I went in for a standard yr. chk-up and was asked to give a urine sample---was happy to---been with dr. for over 15 yrs- I m on several antidep.s--and take highest dose of ibuprofen a day I can for several reasons plus on pain meds of methadone and oxycodone for any break-through as needed that I ONLY take if I truly need it -its 15 mg 4 x day IF I want to take it. pee-cup came up pos for methamphetamines and barbituates--NEVER IN MY LIFE HAVE I TAKEN STUFF LIKE THAT---so he sent it out to lab to specificly test for amphetamines---came back neg--but then also neg for opiates and he now thinks I m not taking my methadone or my oxycodone and will no longer treat my pain-managemant for my nerve damage and the like---if I dont have these meds...even just the methadone ....I wont be able to function the little bit I do now. I have lost the joy of gardening,and mowing my own lawn, plus boating ,riding my bike,and walking far up the hills to pick my berries....I ve reduced so much of my life already, and now he is putting me in this position of possibly not functioning AT ALL if my meds are no longer available. I m to the point of giving up if I cant even get out of bed to do my average daily chores...thats even a challenge.I dont want this on my medical records because it does not state the truth -so how do I go about correcting this mess....I cant sleep -eat-think straight---I m a total basket case over this and any contact with his office gets me 0 response---it s like I was guilty from the start and nothing I say or do or even Beg them to call the lab to look into possible errors or answers gets me nowhere.