Prescription of oxycodone from 5 months ago i was prescribed after a csection if i take ones that are left for pain can i fail a d/t even with script?

"true" true positive: It's highly unlikely your dr documented an oxycodone indication at 5-months post c-section. Based on statistics, the probabilities of aberrant drug behavior in this instance far outweigh the medical possibilities. Regardless of the explanation, this is considered prima fascie evidence for a "true" true positive drug test. Medical theory holds pain from c-section should have resolved, but arguable.

Yes: I would think so if you were taking it for something other than it was prescribed, especially if the area of pain is in a region distinct from initial pain. Usually a bad idea to have those kinds of medications lying around after the condition for its intended use is resolved.