Oral sex, as well as other external forms of pleasure like masturbation, are safe within a few days of childbirth. That is as long as you stay away from the vagina and focus on the area around the clitoris. Other good advice is to be extra careful with stitches and wounds from tearing or episiotomies. This helps to minimise the chance that any bacteria in your partner’s mouth could cause an infection.
You should also remember that placing a tampon (or any other foreign object) inside your vagina to stop the flow of lochia is not advised. That’s because any objects in your vagina before you’re given the all clear by your doctor increase your risk of infections.
If you, and your partner, are comfortable (and have the energy for) oral sex within a few days of childbirth, then you should feel free to go ahead – as long as it stays external, there’s no risk.