I Went to My Po and I Was on Meds He Knew About Them Well I Failed the Drug Test?

i was prescribed muscle relaxers and pain pills along with nerve pills i ha to get a ride to the po office, after the test he asked me to sighn a papper i did i did not know what is was untill i got arrested for a dirty drug test , is my confession good in court with me being on all those meds i told him before i went down there that i was light headed from the meds and would need a ride is this admissable i have a lawyer a very good one what can i do they are trying to make go to a long term rehab
the meds are for a shoulder back injury, i dont even know if my test was pos or not
i think it came back with cocaine in it a dumbd mistake but i have no ideal what i sighned