I Tested Positive for Methamphetamine on a Probation When My PO Knew ?

my MD had me on Adderal for my ADHD. Can’t the drug testing lab tell the difference between legal amphetamine use and illicit meth use? What can I do to clear my name? I’m already suffering the consequencesof this false positive. Probation has refused to order a confirmation test (GC/MS). Please advise.