Tested positive for codeine on a us navy urinalysis. i didn't do drugs. i think its my moms poppy seed cake. it had a pound in it. how do i prove it?

Can't really: Well you can't prove it because that's an example of a true positive test result but from a legal/normal use of poppy. Poppy seeds do actually have codeine in them, so there's no advanced test that will show there's no codeine in the urine, although requesting a "quantitative test" (more expensive) would demonstrate very low levels of urine codeine if just from poppy seeds to support your claim.