Narcotics would be so trace by now that it would be crazy for it to show up.

Either way, you can jump through some hoops. Say you had some intermittent back pain and visited a clinic while travelling. It can be traced, but that requires a lot of effort and time.

edit: Just read that you actually have back pain. I wouldn't worry about it. People take pain meds legally every day. If you only took one it won't yield levels that would be of any concern.