I detoxed myself from 38.5 mgs of methadone..stayed cat 2.5 mgs 10 monthes?

i had to go back to pain mangement,,sevre pains...so she said how much do you take and how long..i said im on the same script you wrote 10 monthes ago..so i took a urine test...no methadone showed up just my xanax im prescibed..why is it that it never showed in my urine?? 2.5 mgs pill form is lowest u can go..and still a potent dose,,but no pain control on this dose..i told her i hate methadone,,been on 160 tops weened down to 2.5 mgs in 3 yrs..by myself..last 38.5 about killed me though..she said im going to give you 2,,5mg perks take 1 every 12 hrs prn only..so here i am wondering why didnt the meth show up in urine drop??????????? she said you wont have to worry about any withdralws..i find this not true even taking perks!! so hers what i need to know..should i waite and gt the methadone out of my systym then start the perks??? also on xanax both scripts..i 4gt to ,ask her things..cvs told mre there shouldnt be any problem even if a bit of meth was in you......NEED INPUT!!!!!!!! THANKS