How Long Does Percocet Remain In The System?

How long dose a percocet stay in the system if u are pregnant i have fibermialga and was percribed them but now that im prego my doc weened me off them and swiched for vikoden but i still take one every so often when i can't deal with the pain so iv been in alot of pain bug i took one monday night anf its now Thursday night and still in alot of pain i kinda want to go to er but im afraid cuzz the urine test will it come up positive? i just took that one pill iv been clean prior to that