This could be due to blood loss during your operation. I would recommend getting a blood count or blood test if possible to see if you're anaemic. It's important that you follow up with your surgeon asap in case there is a more serious underlying issue here.
Itching is a side effect of all narcotics like percocet. If you have itching with alternatives (hydrocodone, codeine and tramadol) you can use something to treat the itch.