Yup it will show up for sure when they test his/her first stool. You need to be honest, and if you're taking such a strong pain killer well you're pregnant and you know it's wrong and they aren't prescribed then you may need to seek some help. I remember when I first came here when I quit using oxy it was a huge help. BUT it's wasn't enough, you need outside help as well. I've been off oxy for a year and a half and still go to AA meetings 2-6 times a week. Seek help for you and your babe. I'm not judging you, honest I've been exactly where you are. Them couple will always turn into a couple more and a couple more and so on....
Is there a reason you were taking pills? The best and safest way is to be truthful with your OB as if there are surprises at birth CPS will step in.