It's going to depend on if you plan on breastfeeding and what method of birth control you are choosing. BC can have a negative affect on your milk production so if breastfeeding it's best to be established prior to starting something. I choose to go on depo after my last daughter and they gave it to me 3 days after I had her when I was discharged from the hospital. I've been on this BC before and new it wouldn't affect my milk production.
6 weeks usually around your 6 week check up
You should get it at your 6 week appointment they want to make sure you are all healed up before starting birth control back up
They usually make you wait the 6 weeks recovery time to make sure your bleeding has stopped etc.
Usually u can right after you have the baby or are fully healed